Parametric Analysis of Silica Extraction Process via Alkaline Fusion and Hydrothermal Desilication Methods from Municipal Solid Waste Bottom Ash Derived from Direct Combustion

Author : Caraos, Neil Aldrin Paul Rosales
Major Adviser : Detras, Monet Concepcion M. 
Committee Members : Migo, Veronica P.; Alfafara, Catalino G.
Year : 2018
Month : June
Type : Thesis
Degree: BS
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In this study, silica extraction from municipal solid waste (MSW) bottom ash obtained from direct combustion was done using two methods: (1) alkaline fusion and (2) hydrothermal desilication. The effects of four (4) factors (alkaline reagent type, alkaline fusion temperature, sample-to-reagent ratio, and dissolution ratio) for the alkaline fusion method and three (3) factors (reagent concentration, extraction time, and reagent volume ratio) for the hydrothermal desilication method on the % silica yield were evaluated. Statistical results show that all factors from each method were significant. For the alkaline fusion method, the alkaline reagent type and sample-to-reagent ratio yielded a positive effect on the response, along with interactions between alkaline reagent type, alkaline fusion temperature, and sample-to-reagent ratio, while the dissolution ratio proved to have a negative effect on the response. For the hydrothermal desilication method, the reagent concentration and extraction time proved to have a positive effect on the response, while the reagent volume had a negative effect. The synthesized silica was analyzed to have a purity of greater than 90 percent for both methods and a particle size ranging from 200 to 300 nanometers. The highest percent yield from the alkaline fusion method was 19.89 %using sodium hydroxide as reagent type, 500 ᵒC fusion temperature, 5:1 reagent ratio, and 100:1 dissolution ratio. The latter method generated 8.85 % silica yield with the reagent concentration of 1.5 M, 30 minutes extraction time, and 20 mL reagent volume ratio. Nonetheless, it cannot be statistically concluded that the alkaline fusion method is the more suited approach for silica extraction; based on a qualitative estimation, however, the alkaline fusion method currently has a more appropriate range of working conditions for optimum silica extraction.

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