Optimization of the metakaolin geopolymer preparation for maximized ammonium adsorption capacity
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Geopolymers are functional materials that can be used in various environmental applications such as adsorbents in pollutant removal from wastewaters. Metakaolin geopolymer (MK-GP) has been proven to be especially suitable for ammonium (NH4 +) removal. In this research, the optimal reagent and raw material ratios in the preparation of MK-GP in terms of NH4 + adsorption capacity were investigated. The response surface methodology based on the face-centered central composite design was used to optimize the levels of three factors: the amounts of hydroxide, silicate, and metakaolin. In addition, the effect of Na or K as the charge-balancing cation was studied. Empirical models were fitted to the experimental data using multiple linear regression. The significance of the models was confirmed by means of analysis of variance. Optimal NH4 + removal efficiency was achieved when the amounts of hydroxide and silicate were maximized, the amount of metakaolin was minimized, and Na-based reagents were used. These trends are most likely a result of optimized conversion of metakaolin into MK-GP.
KeywordsZeolite Adsorption Capacity Geopolymer Natural Zeolite Silicate Solution
This work was supported by the Finnish Funding Agency for Innovation (TEKES) [Grant Number 4096/31/2014, project GeoSorbents]. Authors gratefully acknowledge the contributions of Henrik Romar, Riikka Juhola, Tom Heyninck, Esther Takaluoma, Kai Tiihonen, and Marjukka Hyyryläinen in the laboratory work.
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