Short-term high-temperature calcination effects on the physico-chemical, mineralogical and micromorphological properties of Ca-bentonite from Ünye (Ordu, NE Turkey)

Bentonite, which is commercially well-known industrial material, has been used widely due to its various physico-chemical properties -e.g., high swelling capacity; dispersion into colloid particles; reactions with organic materials; high thermal resistance; low hydraulic conductivity in different applications and may subjected to heat treatment in such industrial applications. Applications of heat treatment can change the physico-chemical and mineralogical properties of bentonite that has an important role to define the usage areas of bentonite. In this study, three Ca-bentonite samples from Ünye (NE Turkey) were calcined up to 1000 °C with 200 °C increments at 25 min. The physico-chemical and mineralogical effects of high temperature loading were evaluated by Simultaneous Differential Scanning Calorimeter and Thermogravimetric Analyzer (STD coupled with TGA), X-Ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM), Brunauer–Emmett–Teller (BET) and Loss on Ignition (LOI) analysis. The results of the experiments show that the dehydration up to 400 °C does not alter the properties of Ca-bentonites significantly; however, the endothermic reactions due to dehydroxylation between 400 °C and 800 °C causes the deformation in the Ca-smectite crystal structure revealed by the collapse of the basal reflection from 14 Å to 10 Å and the gradual disappearance of OH stretching of structural hydroxyl groups and decrease in specific surface area and the closure of micropores.