The hydrothermal synthesis of hydrotalcite by using different partially soluble and insoluble in water mangesium and aluminium components

Abstract

In this work, the influence of different partially soluble and insoluble in water Mg and Al components on the formation of hydrotalcite by using only hydrothermal synthesis was examined. Hydrothermal synthesis duration was 4, 24 and 72 h at 200?C and Mg/Al ratio was equal to 3:1. The starting materials were: 4MgCO3?Mg(OH)2?5H2O, Mg5(CO3)4?(OH)2?4H2O, Al(OH)3 and ?-Al2O3. It was determined that Mg and Al containing compounds have most important influence on the formation of hydrotalcite by hydrothermal conditions. 4MgCO3?Mg(OH)2?5H2O as raw material is not recommendable for the synthesis of hydrotalcite, because even after 24 h of isothermal curing at 200?C temperature hydrotalcite is not formed and magnesium aluminum hydroxide hydrate is dominant in the synthesis products. Besides, initial magnesium containing component is decomposed into magnesium carbonate and hydroxide. It was examined that hydrotalcite is formed already after 4 h of hydrothermal synthesis at 200?C temperature when Mg/Al molar ratio is equal to 3:1 in the Mg5(CO3)4?(OH)2?4H2O - ?-Al2O3/ Al(OH)3 - H2O system. However, together with this compound a fair amount of an intermediate compounds (boehmite and magnesium carbonate) are formed. The duration of isothermal curing determines the formation of a hexagonal plates which are characteristic to hydrotalcite.