Preparation of wollastonite from zeolite-containing rock by solid-phase synthesis

The Tatarsko-Shatrashan zeolite-containing deposit, located in the southwest of the Republic of Tatarstan, contains a large amount of calcite (10-50%) of the total mass of the rock, as well as other minerals - zeolite, opal-cristoballite-tridymite. Such a composition requires an expensive zeolite enrichment process, which significantly affects the cost of the final product. The work proposes the use of zeolite-containing rock for the synthesis of calcium silicates, in particular wollastonite. Calcite - limestone flour (dolomite) was used as a Ca-containing source material in this work; zeolite-containing siliceous rock of the Tatarsko-Shatrashan deposit was used as a silicon-containing material, which also includes a source of calcium in the form of calcite (up to 40%). The solid-phase synthesis process was carried out in a SNOL 1100/7.2 muffle furnace at temperatures of 900 and 1100°C, raising to a given temperature was carried out at a rate of 5 °C/min, holding time was 3 hours. The starting components were mixed in stoichiometric ratios CaO:SiO2=0.7-1.1. The work used a generally accepted method for identifying synthesis products - X-ray quantitative analysis. It has been shown that with a CaO:SiO2 ratio in the range of 0.8-0.9 and isothermal exposure for 3 hours at a temperature of 1100 °C, the highest yield of wollastonite is observed - 67-79%. The morphology of calcium silicate was studied using scanning electron microscopy. The resulting calcium silicate can be characterized as a low aspect ratio sintered product with a shape similar to tabular structures. Wollastonite of this form can be used in the ceramic industry as an effective additive that improves the drying characteristics of ceramic masses.