Geopolymer production from saphane alunite

In this doctoral study, the structure of the Şaphane alunite was evaluated for geopolymer synthesis due to its high alumina content. In the study alunite was mixed with NaOH and calcined at 550º C, sulfate in alunite was turned into water soluble sodium sulfate (Na2SO4) salt. Sodium sulfate was removed and then washed at 60 ºC. Sulfate reduced alunite geopolymer prescriptions have been developed. Alkali activation process was applied at different pH and temperature values and geopolymeric materials with different chemical compositions were obtained During the experimental studies, X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX), FTIR Fourier transform infrared (FTIR) and 27Al-Magic Angle Spinning Nuclear magnetic resonance (27Al-MAS NMR) techniques were used. In XRD analysis the amorphous regions of the geopolymer material whereas in FTIR analysis the Si-O-Al bonds and in 27Al MAS NMR analysis AlO4 molecular structure was determined. Physical tests such as water absorption, porosity, compressive strength, flextural strength, freeze - thaw resistance were applied on geopolymer materials and it was observed that the synthesized material remained within the expected qualitative limits. The strength values were increased with using blast furnace slag reinforcement in geopolymeric structures. Whereas the highest compressive strength obtained without blast furnace slag for geopolymeric material was 48 MPa, this value for blast furnace slag was 75 MPa. Keywords: Geopolymerization; Alunite; XRD; FTIR, 27Al MAS NMR analysis