Publicação
Production of geopolymers from fly ash for wastewater treatment
| Resumo: | Rapid waste generation presents environmental, economic, and social challenges. The circular economy concept aims to reintegrate waste into production cycles, including municipal solid waste (MSW). Geopolymers (GPs) derived from MSW ash offer valuable applications, especially as cost-effective and environmentally friendly adsorbents. This study focuses on developing geopolymeric adsorbents using MSW fly ash (FA) as a precursor and evaluating their efficacy in treating wastewater containing gallic acid (GA). Specific objectives include characterizing the FA, optimizing geopolymer production through a Design of Experiment, and assessing the performance of the produced GPs as adsorbents. The experimental design in this study employed a Box-Behnken design (BBD) with three key factors: Si/Al mass ratio, NaOH molar concentration, and Na2SiO3/NaOH mass ratio. Material characterization was conducted using ICP-OES, porosimetry and surface area analysis, FT-IR, SEM, XRD, acid-base character, and pHpzc determination. Adsorption tests included studying the kinetics using pseudo-first-order and pseudo-second-order models and intraparticle diffusion. Equilibrium isotherms were analyzed using the Freundlich and Langmuir models. Statistical analysis indicated the Si/Al ratio as the most significant factor for GA removal. Characterization of the GPs and FA revealed FA's composition as a suitable source for aluminosilicate synthesis. Porosimetry and surface area analysis demonstrated substantial improvements in the GPs compared to FA, with GP-13 exhibiting the largest surface area equal to 61 m²/g. FT-IR analysis confirmed geopolymerization, while SEM analysis revealed structural variations between the GPs and unreacted FA particles in the GPs. XRD analysis confirmed the amorphous nature of the produced materials and the predominance of calcite. Acid-base characterization demonstrated the basic nature of the GPs, with pHpzc values around 8, showing that electrostatic attraction between the positively charged GPs and GA contributed significantly to the adsorption process. Adsorption kinetics revealed a favorable fit to the pseudo-first-order model, with rapid initial adsorption reaching equilibrium at approximately 200 minutes. Equilibrium studies favored the Freundlich model, indicating favorable adsorption conditions with a significant affinity between GA and the GPs. GP-6 exhibited the highest maximum adsorption capacity of 75.839 mg/g. In conclusion, all the produced GPs showed efficiency to adsorb GA. |
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| Autores principais: | Natal, Ana Paula Silva |
| Assunto: | Geopolymers Municipal solid waste Fly ash Adsorption Circular economy |
| Ano: | 2023 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Instituto Politécnico de Bragança |
| Idioma: | inglês |
| Origem: | Biblioteca Digital do IPB |
| Resumo: | Rapid waste generation presents environmental, economic, and social challenges. The circular economy concept aims to reintegrate waste into production cycles, including municipal solid waste (MSW). Geopolymers (GPs) derived from MSW ash offer valuable applications, especially as cost-effective and environmentally friendly adsorbents. This study focuses on developing geopolymeric adsorbents using MSW fly ash (FA) as a precursor and evaluating their efficacy in treating wastewater containing gallic acid (GA). Specific objectives include characterizing the FA, optimizing geopolymer production through a Design of Experiment, and assessing the performance of the produced GPs as adsorbents. The experimental design in this study employed a Box-Behnken design (BBD) with three key factors: Si/Al mass ratio, NaOH molar concentration, and Na2SiO3/NaOH mass ratio. Material characterization was conducted using ICP-OES, porosimetry and surface area analysis, FT-IR, SEM, XRD, acid-base character, and pHpzc determination. Adsorption tests included studying the kinetics using pseudo-first-order and pseudo-second-order models and intraparticle diffusion. Equilibrium isotherms were analyzed using the Freundlich and Langmuir models. Statistical analysis indicated the Si/Al ratio as the most significant factor for GA removal. Characterization of the GPs and FA revealed FA's composition as a suitable source for aluminosilicate synthesis. Porosimetry and surface area analysis demonstrated substantial improvements in the GPs compared to FA, with GP-13 exhibiting the largest surface area equal to 61 m²/g. FT-IR analysis confirmed geopolymerization, while SEM analysis revealed structural variations between the GPs and unreacted FA particles in the GPs. XRD analysis confirmed the amorphous nature of the produced materials and the predominance of calcite. Acid-base characterization demonstrated the basic nature of the GPs, with pHpzc values around 8, showing that electrostatic attraction between the positively charged GPs and GA contributed significantly to the adsorption process. Adsorption kinetics revealed a favorable fit to the pseudo-first-order model, with rapid initial adsorption reaching equilibrium at approximately 200 minutes. Equilibrium studies favored the Freundlich model, indicating favorable adsorption conditions with a significant affinity between GA and the GPs. GP-6 exhibited the highest maximum adsorption capacity of 75.839 mg/g. In conclusion, all the produced GPs showed efficiency to adsorb GA. |
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