Natural zeolite clinoptilolite was calcined at different temperatures (700–1000 °C) in order to increase its reactivity as geopolymer precursor. The clinoptilolite structure was completely destructed at 900 °C and the material was called “metazeolite”. Geopolymer pastes were prepared with different SiO₂/Al₂O₃ ratio by using silicate and aluminate activators, including alkaline waste solution from a Dutch aluminium anodizing industry. The prepared geopolymers were cured at 80 °C and were characterized by XRD, FTIR and SEM. The metazeolite based geopolymer activated with potassium silicate solution possessed the highest compressive strength (43 MPa ± 4 MPa). The silicate and hydroxide activated geopolymers showed relatively high shrinkage. On the other hand, by using aluminate solutions the shrinkage of geopolymers was significantly decreased. The aluminate activated geopolymer contained newly formed phillipsite and zeolite Na-P. However, there was no significant difference in geopolymer product when using chemical grade aluminate solutions and industrial waste aluminate solutions. The use of alkaline waste solutions is recommended because of economic and environmental benefits.

One of the potential raw materials for preparation of geopolymers is the natural zeolite. In the present report, the used natural zeolite (clinoptilolite) is from huge deposit near Beli Plast, Bulgaria. Geopolymer pastes and mortars are prepared by using three different alkaline activators—sodium hydroxide, sodium silicate and sodium carbonate. The hardened geopolymers are tested for determination of mechanical properties by traditional standardized methods. The structure and the composition of the materials are studied by direct physical methods—X-ray diffraction (XRD), thermal analysis (DTA and TGA) and scanning electron microscopy (SEM). The results show variable degree of dissolutions of the raw zeolite material when using different activators and formation of solid geopolymer materials with qualitatively different structure. Despite its relatively low compressive strength, geopolymers based on natural zeolite cured at room temperature and used as coating, show very good adhesion to concrete.