Microchemistry and microstructure of sustainable mined zeolite-geopolymer

Geopolymers are three-dimensional amorphous Si-O-Al networks that generally can be synthesized from low-Ca aluminosilicate mineral sources. Such materials were first introduced as a sustainable construction material but today their application goes beyond the building industry. So far, a broad range of aluminosilicate minerals including fly ash, natural pozzolans, kaolin and metakaolin have been used to produce geopolymers; however, there are limited studies on the geopolymerization of porous and crystalline aluminosilicate minerals such as mined zeolites. Use of zeolite as it is for commercial applications depends on the shape and architecture of these materials. Therefore, the hypothesis was that geopolymerization provides the possibility of using mined zeolite in different shapes. Moreover, zeolite as a nontoxic mineral material with an inherent 3D structure may result in the formation of the cleaner geopolymeric product with different physical properties compared to when waste materials such as fly ash are employed. In this study, the viability of creating geopolymers from mined zeolite has been demonstrated. The aim of this study was to evaluate the influence of different parameters such as zeolite particle size, curing temperature, reagents ratio and time on amorphous content and mechanical strength. The conversion of the crystalline phase of mined zeolite to amorphous gel and/or synthetic zeolite phases was comprehensively studied using X-ray diffraction. It was found that finer zeolite particles resulted in the formation of a material with higher amorphous content (max ∼60%) and higher mechanical strength (max ∼33 MPa). It was also shown that the higher amorphous content did not necessarily translate to higher mechanical strength due to the formation of intermediate species that cannot transfer into the polycondensation stage. It was revealed that the formation of analcime and chabazite may occur through the geopolymerization process. Microstructure studies using infrared spectroscopy confirmed the geopolymer formation and development over time.