Combined Influence of Low-Grade Metakaolins and Natural Zeolite on Compressive Strength and Heavy Metal Adsorption of Geopolymers
authors Sudagar, AJ; Andrejkovicova, S; Rocha, F; Patinha, C; Soares, MR; Velosa, AL; da Silva, EF
nationality International
journal MINERALS
author keywords geopolymer; metakaolin; zeolite; heavy metals; adsorption; compressive strength; low grade
abstract Metakaolins (MKs) prepared from low-grade kaolins located in the Alvaraes (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 SiO2/Al2O3 and Na2O/Al2O3 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 (Cd2+, Cr3+, Cu2+, Pb2+, and Zn2+) adsorption tests exhibit relatively higher adsorption capacities of Barqueiros MK-based geopolymers for all the heavy metals except Cd2+. 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 Alvaraes MK-based geopolymers. The general trend of adsorption of the heavy metals of both MK-based geopolymers is Pb2+ > Cd2+ > Cu2+ > Zn2+ > Cr3+ when fitted by the Langmuir isotherm adsorption model. The MK and zeolite characteristics influence geopolymers' structure, strength, and adsorption capacities.
publisher MDPI
isbn 2075-163X
year published 2021
volume 11
issue 5
digital object identifier (doi) 10.3390/min11050486
web of science category 19
subject category Geochemistry & Geophysics; Mineralogy; Mining & Mineral Processing
unique article identifier WOS:000662402600001
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