Characterization of rice hull ash

Abstract

Rice hulls, a byproduct of the rice industry, contain 60 -90% silica and are unique within nature. The annual worldwide output of rice-hull-derived silica is more than 3.2 million tons, which poses environmental concerns because of disposal issues. Burning rice hulls, as a preparative step for energy production, is a useful solution to the growing environmental concern, a desirable outcome would be the economic use of the resulting silica-rich hull ash. The economical usefulness of this silica ash in the filler market has been undermined by its limited dispersion abilities and poor interaction capability with polymers. In this study, some of the reasons for the poor performance of silica ash as a reinforcing filler in various polymeric composites were linked to its inherent characteristics: factors such as its impurity, irregular topography, porosity, and chemical and thermodynamic nature arising from its surface polarity that negatively influence the filler-matrix interactions. The silica ash obtained from a novel combustion process had about 6% (w/w) impurity, of which around 3% was volatile. We also propose that the silanation efficiency of silica ash is lower compared to other commercial silicas because of its porosity, which could hide a fraction of the silane used. Also, processing changed the particle size distribution, and this could have affected the agglomerating tendencies and seriously marked the reinforcing capabilities of the silica ash. The estimation of the surface silanol groups of the rice hull ash by thermogravimetric studies indicated that the surface silanol density was about 16/nm 2 . On a comparative scale, this value is comparable to the silanol density on precipitated silica, but a thermodynamic study of silica ash surface revealed a high surface free energy that contributed to its high aggregation tendencies and poor distribution and dispersion abilities.

Silica nano-particles produced by worms through a bio-digestion process of rice husk

“…4(d) where the sizes of all samples are shown. For comparison purposes, some results are reported for the production of silica particles obtained feeding worms with others two agro-industrial wastes which contain silica: coffee (12%) and cane (8%) husk; the content of silica of these husks is lower respect to rice husk but high enough as to be also restricted to massive applications [9,16,[21][22][23]. These particles were obtained following a similar process as the one reported for rice husk.…”

“…As fuel produces large amount of ashes, partial combustion and low efficiency, leading to smoke emissions. The disposal of the ashes and partially burned husks creates environmental hazards [8,9]. Due this, important research work has being oriented to find new and important applications of this pollutant; one of the most important, besides the use as fuel, is the manufacture of construction materials due to its properties of flame retardant.…”

Lightweight bricks manufactured from water treatment sludge and rice husks

“…Many industrial applications include refractory brick manufacturing, concrete and lightweight building materials, and the manufacture of insulation, flame retardants, etc. [22][23][24][25]. Although rice husk ash applications in cement and steel manufacturing are well established, silica-enriched ash is usually produced by burning the rice husks.…”

Fly Ash Pollutants, Treatment and Recycling

“…In heat generation, rice husk has a calorific value of 12.1-15.2 MJ/kg (Beagle 1981). Rice husk has a chemical composition varying from sample to sample, depending upon the varieties of paddy sown, geographical conditions, soil chemistry, proportion of irrigated area, fertilizer used, climatic variation, timeliness of crop production operations and agronomic practices in the paddy growth process (Chaudhary and Jollands 2004;DSIRI 1992;Rao 1980;Patel et al 1987). Rice husk major constituents comprising of cellulose, hemicellulose, lignin, hydrated silica (Chandrasekhar et al 2005), which the exterior composed a large amount of silica (Mahin 1990;Ismail and Waliuddin 1996).…”