Combined Influence of Low-Grade Metakaolins and Natural Zeolite on Compressive Strength and Heavy Metal Adsorption of Geopolymers

Abstract

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 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 Alvarães 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.

Natural Radioactivity in Raw Building Materials for Underground Parking Lots and Assessment of Radiological Health Risk for the Population

“…The third cluster is composed of G4 and G6, with a positive correlation with C Ra-226 and I α in terms of PC1, and a negative correlation with all the variables in terms of PC2. The different behavior evidenced by the PCA algorithm can be strictly dependent on the chemical composition and mineralogical nature of the investigated raw building materials for underground parking lots [ 56 , 57 , 58 ].…”

“…The different behavior evidenced by the PCA algorithm can be strictly dependent on the chemical composition and mineralogical nature of the investigated raw building materials for underground parking lots [56][57][58]. Noteworthily, G4, and G6 showed negative correlations with all the variables, and thus, they could be considered as those showing the best characteristics, the most reassuring from the radiation protection point of view, with the understanding that, as extensively reported above, all of the investigated samples appeared to be nonhazardous to humans.…”

Investigation of the composition and morphology of raw materials from the Aral Sea region

“…In the processed metakaolin minerals group, it can be observed that elements such as Na, Fe, and Ti are present in meagre amounts compared to Al, Si, and O, respectively. [49]. Therefore, it is con rmed that the predominant phase results in silicon dioxide (SiO 2 ) and Aluminium oxide (Al 2 O 3 ) compounds with the addition of other elemental impurities, namely Na, V, Fe, Ti, Mg, Ca, S, etc., [50] which is also consistent with the functional analysis done by FTIR measurements.…”

Synthesis of Electrolytic Manganese Slag–Solid Waste-Based Geopolymers: Compressive Strength and Mn Immobilization

“…After mixing with fly ash at the ratio of 3:2, a geopolymer of 16 MPa was produced at 15 MPa, which demonstrated good environmental stability and leaching toxicity in accordance with the national standard. Meanwhile, the related experiments showed that the geopolymer had better performance in heavy metal curing [22][23][24]. In recent years, even though there have been many attempts to use EMR, the consumption of EMR is still relatively low [25].…”