Optimization of High-purity Silica Production from Rice Hull Ash by Citric Acid Leaching

Author : Pamplona, Juan Miguel Ortiona
Major Adviser : Doliente, Stephen S. 
Committee Members : Alfafara, Catalino G.; Detras, Monet Concepcion M. 
Year : 2017
Month : June
Type : Thesis
Degree: BS
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Optimization of the incineration temperature, citric acid concentration, and stirring time of solution to maximize silica purity was performed employing a Box-Behnken experimental design. X-Ray fluorescence analysis was done to quantify the silica content and metallic impurities present in RHA. Results of statistical analysis show that all three factors have significant effects on the purity of silica, as well as the quadratic effect of temperature and interaction effect of combustion temperature and stirring time. All main factors caused a positive effect on silica purity. However, at higher incineration temperature, silica purity slightly decreased because of the possible eutectic reaction of alkali metals with silica. Numerical optimization was done and the optimum values obtained were incineration temperature of 657.27°C, acid concentration of 6.93 %wt, and stirring time of 31.96 minutes. A confirmatory experiment was performed and the silica recovered had 99.41% purity. Characterization results demonstrated that nanosilica synthesized from high purity silica produced at optimum conditions were in amorphous form and the average particle size were in the range of 85.5 nm to 154 nm.

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