Optimization and Characterization of Silica Synthesized from Rice Husk
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Date
2019-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
Rice husks are agricultural biomass waste, which is considered as renewable resources that
are produced every year in Ethiopia. Despite of its non-commercial value and causing
environmental pollutions, its ash content is rich in silica (SiO2) and becomes an economic
potential source. This study aims at utilizing this agricultural biomass waste into valuable
product, silica. Silica (SiO2) was prepared by using rice husk ash (RHA) as a source of
silicate (SiO
-2
3) . Then further reaction of the ash with NaOH has formed Sodium silicate
(Na2SiO3) solution. Then, titration of this solution with HCl forms the precipitation of silicagel.
The
effect
of
acid
pretreatment
on
the
removal
of
metallic
impurities
and
its
percentage
purity
as well as on the properties of RHA was examined using Atomic Absorption
Spectrophotometer (AAS). The percentage purity of SiO2 in the untreated RH were found
87.1% with some metallic impurities and 97.6% purity of silica is obtained from the treated
RH, which proved to be effective in removing the metallic impurities to a very lower level
and enhance the purity of silica in the RHA. The experiment and statistical analysis for the
production of SiO2 were designed using three-level-three-factor BBD for the total run of 17
experiments at operating process conditions of acid concentration (1-2N), pyrolysis
temperature (450-850C) and Pyrolysis time (1-5h). The optimal %yield were found to be
98.971% with 98.6% purity of SiO2% at conditions for 1.95N pretreatment acid
concentration,658C pyrolysis temperature, and 4.95h pyrolysis time. The effects of
combustion temperature and time on % yield and the structural properties of silica in the ash
were also characterized using XRD and FTIR analysis. The quality of the extracted silica
were determined and characterized by its physico chemical properties. Furthermore, the silica
obtained from RH was compared with the commercial silica. As a result, they perform
equivalency with commercially available. Also, from optimized conditions, surface area of
the synthesized silica was found 779.7m
2
/g in amorphous form.
Description
Keywords
Rice husk, Rice husk ash, RHAs, Sodium silicate, Silica