Determination of Zeolite NaA (LTA) Synthesis Parameters from Technogenic Silica Gel for Water Softening

Utilization of fluoride-containing waste from aluminium fluoride production is an important strategic issue. Here, we use technogenic silica gel containing about 30 wt. % of fluoride and aluminum for zeolite NaA (LTA) synthesis. The process consists of two steps: silica gel acid purification up to a silica content of 95 wt. % and hydrothermal synthesis. X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy were used for phase identification and synthesis conditions optimization. As a result, we determined that hydrothermal synthesis from aluminosilicate gel with molar ratios SiO₂:Al₂O₃ = 1.8, Na₂O:Al₂O₃ = 4.0, and H₂O:SiO₂ = 50 at 95 °C for 60 min with vigorous stirring yields zeolite NaA with Ca²⁺ and Mg²⁺ ion exchange capacities of 562.6 and 187.5 mEq/100 g respectively and water vapor capacity of 25.8 g/100 g. Thus, the developed process offers waste silica gel utilization and production of zeolite NaA, which is as good as commercial analogs.