Development and characterization of clinoptilolite-, mordenite-, and analcime-based geopolymers: A comparative study

This study examines the development of geopolymers from clinoptilolite, mordenite, and analcime and compares the properties of the resulting green-binding materials. Sodium silicate and sodium hydroxide solutions were used as activators. Compressive-strength, X-ray diffractometer (XRD), and scanning electron microscopy (SEM/EDX) analysis were employed to characterize the mechanical development, mineralogical composition, and microstructure of the geopolymers. The results show that clinoptilolite, mordenite, and analcime were found to offer much potential for the synthesis of geopolymers. Clinoptilolite-based geopolymer is the most reactive of the three and generates a higher rate of geopolymerization than mordenite- and analcime-based geopolymers. Reactive components other than zeolites are also found to be critical to the geopolymerization reaction. Feldspar provides additional Na for the reaction, reinforcing the gel structure and developing better compressive strength. The difference in the mechanical and microstructural properties of natural zeolite-based geopolymers is attributed to the varying nature and mineralogical content of the starting materials. Different gel characteristics provide valuable information on the role of the active phases involved in the reaction.