PHASE TRANSFORMATIONS IN THE PRODUCTION OF CALCIUM SILICATE FROM ZEOLITE-SILICA ROCK

Phase transformations in the zeolite-containing rock – calcite system during the synthesis of wollastonite in a temperature range of 800 to 1200 °C are studied. The components were mixed in a CaO/SiO2 ratio of 0.7, and then, in order to increase the contact area of the phases, grinding was performed in a Fritsch Pulverisette 5/2 planetary mill for 5 min at 200 rpm. Solid-phase synthesis was carried out in SNOL 1100/7.2 and Nabertherm LH 120/13 muffle furnaces at temperatures ranging from 800 to 1200 °C with intervals of 50 °C and an isothermal holding time of 1 to 4 h. The phase composition of the component firing products is quantitatively evaluated by quantitative X-ray analysis. The process of wollastonite formation proves to begin at temperatures ranging between 800 and 900 °C. A smooth growth of calcium metasilicate content continues up to 1100 °C, and wollastonite becomes the main product at this temperature. The maximum yield of wollastonite (81%) is reached at 1175 °C isothermal holding for 3 hours. The temperature of phase transition from β- to α-wollastonite has been experimentally found to be 1190 °C.