In this research a hydrothermal method was applied to the synthesis of wollastonite. Silica, nano silica and calcium carbonate were used as the main raw materials and sodium chloride as a mineralizer. Six different slurries were prepared with SiO2/CaO molar ratios of 0.54, 0.8, 1 and a solid content of 50 wt%. Then the slurries were hydrothermally treated in an autoclave for 12 h at 130 οC at a pressure of 1.5 atm. In the next step, the samples were dried at 150 οC for 8 h and then calcined at 1000 οC for 5 h. The microstructures and phases analyses were investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Finally a three-stage mechanism was proposed for the hydrothermal synthesis of wollastonite. The results showed that by using nano silica, fine grain wollastonite was obtained.

Keywords: Silica, Nano silica, Wollastonite, Hydrothermal synthesis, Mechanism.