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.

中文翻译：

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低品位偏高岭土和天然沸石对地质聚合物抗压强度和重金属吸附的综合影响

由位于葡萄牙阿尔瓦良斯（A）和巴尔克罗斯（B）地区的低级高岭土制备的偏高岭土（MK）被用作铝硅酸盐来源，以比较它们对地质聚合物的抗压强度和重金属吸附的影响。天然沸石是一种廉价，高效的吸附剂，被用作配方中的添加剂，以增强地质聚合物的吸附能力并减少MK利用的环境足迹。合成了地聚物，其中用高达75 wt。％的沸石代替MK（A25，B25-25％MK 75％沸石； A50，B50-50％MK 50％沸石； A75，B75-75％MK 25％沸石； A100，B100-100％MK）。SiO ₂ / Al ₂ O ₃与Na ₂ O / Al ₂ O ₃的摩尔比保持在1以减少硅酸钠和氢氧化钠对环境的影响。使用X射线衍射分析鉴定了地质聚合物的晶体学。通过扫描电子显微镜观察表面形态以了解沸石掺入的效果。使用X射线荧光光谱和能量色散X射线光谱进行化学分析可得出有关地质聚合物的Si / Al比的信息。固化1、14和28天后获得的地质聚合物的抗压强度值表明，具有100％MK的地质聚合物具有较高的强度（A100-15.4 MPa； B100-32.46 MPa）。因此，沸石无助于两种基于MK的地质聚合物的抗压强度的提高。重金属（Cd 2 ⁺，Cr ³⁺，Cu 2 ⁺，Pb²⁺和Zn ²⁺）吸附测试显示，Barqueiros MK基地质聚合物对除Cd ²⁺以外的所有重金属的吸附能力相对较高。而且，沸石对由Barqueiros MK生产的地质聚合物上的二价阳离子的吸附产生了积极影响，因为B75表现出最高的吸附能力，但是对于AlvarãesMK基地质聚合物却没有观察到这种影响。两种基于MK的地质聚合物对重金属的吸附的总体趋势为Pb ²⁺ > Cd ²⁺ > Cu ²⁺ > Zn ²⁺ > Cr ³⁺当由Langmuir等温线吸附模型拟合时。MK和沸石的特性会影响地质聚合物的结构，强度和吸附能力。