Synthesis of type A zeolite from mechanoactivated metakaolin mixtures

Abstract

The zeolite A was synthesized from the mechanically activated solid mixtures of metakaolin, sodium hydroxide and aluminum oxide. The stages of both thermal treatment and hydrothermal crystallization were investigated and optimized. The size of zeolite A particle was directly measured by scanning electron microscopy as well as calculated using the X-ray diffraction spectroscopy data. The thermal stability of the zeolite A was studied by the differential thermal analysis. It was shown that the optimum thermal treatment temperature providing the zeolite A yield of about 65 wt% and the particle size in the range of 0.2–0.3 μm is 600 °C. The furthermore increase in the thermal treatment temperature results in decreasing amount of zeolite A crystalline phase as well as in the formation of nepheline. It was also found that the optimum NaOH concentration providing the zeolite A yield of about 90 wt % and the particle size more than 0.7 μm after the hydrothermal crystallization stage is 2–4 mol/l. The higher alkali concentrations result decreasing amount of the zeolite A phase and cause the recrystallization into the sodalite. The use of KOH in the hydrothermal crystallization stage allows one to obtain the potassium-containing zeolite A by direct synthesis.