Synthesis of Zirconosilicates under High-Alkaline Conditions

Synthesis of zirconosilicates from a stoichiometric mixture of Na2CO3, CaO, Fe2O3, ZrOCl2, and SiO2 with the Na : Ca : Fe : Zr : Si ratio belonging to the compositional area of eudialyte-geoup minerals (EGM), was carried out under high-alkaline conditions (in the presence of 1 M aqueous solutions of NaCl and 46% NaOH) at a temperature of 600 °C and a pressure of 2 kbar, for 10 days. In some experiments, natural raslakite (a Ca-deficient EGM) was used as a seed added in amount of 2 wt % of the whole charge. According to electron microprobe analyses, powder X-ray diffraction data and IR spectroscopy, high-alkaline EGM, zirsinalite, parakeldyshite, and aegirine were identified in the products of the syntheses carried out using a charge with relatively high Si : Zr, Fe : Zr and Na : Zr ratios. At relatively low values of these ratios, no EGM formed.