Combined Influence of Low-Grade Metakaolins and Natural Zeolite on Compressive Strength and Heavy Metal Adsorption of Geopolymers
Metakaolins (MKs) prepared from low-grade kaolins located in the Alvarães (A) and Barqueiros (B) regions of Portugal were used as the aluminosilicate source to compare their effect on the compressive strength and heavy metal adsorption of geopolymers. Natural zeolite, an inexpensive, efficient adsor...
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| Format: | Article |
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MDPI AG
2021-05-01
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| Series: | Minerals |
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| Online Access: | https://www.mdpi.com/2075-163X/11/5/486 |
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| author | Alcina Johnson Sudagar Slávka Andrejkovičová Fernando Rocha Carla Patinha Maria R. Soares Ana Luísa Velosa Eduardo Ferreira da Silva |
| author_facet | Alcina Johnson Sudagar Slávka Andrejkovičová Fernando Rocha Carla Patinha Maria R. Soares Ana Luísa Velosa Eduardo Ferreira da Silva |
| author_sort | Alcina Johnson Sudagar |
| collection | DOAJ |
| description | Metakaolins (MKs) prepared from low-grade kaolins located in the Alvarães (A) and Barqueiros (B) regions of Portugal were used as the aluminosilicate source to compare their effect on the compressive strength and heavy metal adsorption of geopolymers. Natural zeolite, an inexpensive, efficient adsorbent, was used as an additive in formulations to enhance geopolymers’ adsorption capacities and reduce MK utilization’s environmental footprint. Geopolymers were synthesized with the replacement of MK by zeolite up to 75 wt.% (A25, B25—25% MK 75% zeolite; A50, B50—50% MK 50% zeolite; A75, B75—75% MK 25% zeolite; A100, B100—100% MK). The molar ratios of SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> and Na<sub>2</sub>O/Al<sub>2</sub>O<sub>3</sub> were kept at 1 to reduce the sodium silicate and sodium hydroxide environmental impact. Geopolymers’ crystallography was identified using X-ray diffraction analysis. The surface morphology was observed by scanning electron microscopy to understand the effect of zeolite incorporation. Chemical analysis using X-ray fluorescence spectroscopy and energy dispersive X-ray spectroscopy yielded information about the geopolymers’ Si/Al ratio. Compressive strength values of geopolymers obtained after 1, 14, and 28 days of curing indicate high strengths of geopolymers with 100% MK (A100—15.4 MPa; B100—32.46 MPa). Therefore, zeolite did not aid in the improvement of the compressive strength of both MK-based geopolymers. The heavy metal (Cd<sup>2+</sup>, Cr<sup>3+</sup>, Cu<sup>2+</sup>, Pb<sup>2+</sup>, and Zn<sup>2+</sup>) adsorption tests exhibit relatively higher adsorption capacities of Barqueiros MK-based geopolymers for all the heavy metals except Cd<sup>2+</sup>. Moreover, zeolite positively influenced divalent cations’ adsorption on the geopolymers produced from Barqueiros MK as B75 exhibits the highest adsorption capacities, but such an influence is not observed for Alvarães MK-based geopolymers. The general trend of adsorption of the heavy metals of both MK-based geopolymers is Pb<sup>2+</sup> > Cd<sup>2+</sup> > Cu<sup>2+</sup> > Zn<sup>2+</sup> > Cr<sup>3+</sup> when fitted by the Langmuir isotherm adsorption model. The MK and zeolite characteristics influence geopolymers’ structure, strength, and adsorption capacities. |
| first_indexed | 2024-03-10T11:45:37Z |
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| issn | 2075-163X |
| language | English |
| last_indexed | 2024-03-10T11:45:37Z |
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| spelling | doaj.art-c8b256a70d8741f49243de939c8da17a2023-11-21T18:10:22ZengMDPI AGMinerals2075-163X2021-05-0111548610.3390/min11050486Combined Influence of Low-Grade Metakaolins and Natural Zeolite on Compressive Strength and Heavy Metal Adsorption of GeopolymersAlcina Johnson Sudagar0Slávka Andrejkovičová1Fernando Rocha2Carla Patinha3Maria R. Soares4Ana Luísa Velosa5Eduardo Ferreira da Silva6Geosciences Department, Geobiotec Research Unit, Campus Universitário de Santiago, University of Aveiro, 3810-193 Aveiro, PortugalGeosciences Department, Geobiotec Research Unit, Campus Universitário de Santiago, University of Aveiro, 3810-193 Aveiro, PortugalGeosciences Department, Geobiotec Research Unit, Campus Universitário de Santiago, University of Aveiro, 3810-193 Aveiro, PortugalGeosciences Department, Geobiotec Research Unit, Campus Universitário de Santiago, University of Aveiro, 3810-193 Aveiro, PortugalCICECO & LCA, Campus Universitário de Santiago, University of Aveiro, 3810-193 Aveiro, PortugalCivil Engineering Department, RISCO, Campus Universitário de Santiago, University of Aveiro, 3810-193 Aveiro, PortugalGeosciences Department, Geobiotec Research Unit, Campus Universitário de Santiago, University of Aveiro, 3810-193 Aveiro, PortugalMetakaolins (MKs) prepared from low-grade kaolins located in the Alvarães (A) and Barqueiros (B) regions of Portugal were used as the aluminosilicate source to compare their effect on the compressive strength and heavy metal adsorption of geopolymers. Natural zeolite, an inexpensive, efficient adsorbent, was used as an additive in formulations to enhance geopolymers’ adsorption capacities and reduce MK utilization’s environmental footprint. Geopolymers were synthesized with the replacement of MK by zeolite up to 75 wt.% (A25, B25—25% MK 75% zeolite; A50, B50—50% MK 50% zeolite; A75, B75—75% MK 25% zeolite; A100, B100—100% MK). The molar ratios of SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> and Na<sub>2</sub>O/Al<sub>2</sub>O<sub>3</sub> were kept at 1 to reduce the sodium silicate and sodium hydroxide environmental impact. Geopolymers’ crystallography was identified using X-ray diffraction analysis. The surface morphology was observed by scanning electron microscopy to understand the effect of zeolite incorporation. Chemical analysis using X-ray fluorescence spectroscopy and energy dispersive X-ray spectroscopy yielded information about the geopolymers’ Si/Al ratio. Compressive strength values of geopolymers obtained after 1, 14, and 28 days of curing indicate high strengths of geopolymers with 100% MK (A100—15.4 MPa; B100—32.46 MPa). Therefore, zeolite did not aid in the improvement of the compressive strength of both MK-based geopolymers. The heavy metal (Cd<sup>2+</sup>, Cr<sup>3+</sup>, Cu<sup>2+</sup>, Pb<sup>2+</sup>, and Zn<sup>2+</sup>) adsorption tests exhibit relatively higher adsorption capacities of Barqueiros MK-based geopolymers for all the heavy metals except Cd<sup>2+</sup>. Moreover, zeolite positively influenced divalent cations’ adsorption on the geopolymers produced from Barqueiros MK as B75 exhibits the highest adsorption capacities, but such an influence is not observed for Alvarães MK-based geopolymers. The general trend of adsorption of the heavy metals of both MK-based geopolymers is Pb<sup>2+</sup> > Cd<sup>2+</sup> > Cu<sup>2+</sup> > Zn<sup>2+</sup> > Cr<sup>3+</sup> when fitted by the Langmuir isotherm adsorption model. The MK and zeolite characteristics influence geopolymers’ structure, strength, and adsorption capacities.https://www.mdpi.com/2075-163X/11/5/486geopolymermetakaolinzeoliteheavy metalsadsorptioncompressive strength |
| spellingShingle | Alcina Johnson Sudagar Slávka Andrejkovičová Fernando Rocha Carla Patinha Maria R. Soares Ana Luísa Velosa Eduardo Ferreira da Silva Combined Influence of Low-Grade Metakaolins and Natural Zeolite on Compressive Strength and Heavy Metal Adsorption of Geopolymers Minerals geopolymer metakaolin zeolite heavy metals adsorption compressive strength |
| title | Combined Influence of Low-Grade Metakaolins and Natural Zeolite on Compressive Strength and Heavy Metal Adsorption of Geopolymers |
| title_full | Combined Influence of Low-Grade Metakaolins and Natural Zeolite on Compressive Strength and Heavy Metal Adsorption of Geopolymers |
| title_fullStr | Combined Influence of Low-Grade Metakaolins and Natural Zeolite on Compressive Strength and Heavy Metal Adsorption of Geopolymers |
| title_full_unstemmed | Combined Influence of Low-Grade Metakaolins and Natural Zeolite on Compressive Strength and Heavy Metal Adsorption of Geopolymers |
| title_short | Combined Influence of Low-Grade Metakaolins and Natural Zeolite on Compressive Strength and Heavy Metal Adsorption of Geopolymers |
| title_sort | combined influence of low grade metakaolins and natural zeolite on compressive strength and heavy metal adsorption of geopolymers |
| topic | geopolymer metakaolin zeolite heavy metals adsorption compressive strength |
| url | https://www.mdpi.com/2075-163X/11/5/486 |
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