Physico-Chemical Properties of Synthetic Hydrotalcites in Relation to Composition

Abstract

Abstract Hydrotalcite solid solutions were prepared by coprecipitation followed by hydrothermal treatment between 150° and 250°C. Based on the structural formula [Mg 1−x Al x (OH) 2 ] x+ [(CO 3 ) x/2 • mH 2 O] x− , pure solid solutions were formed in the range A1/(A1 + Mg) = 0.2 to 0.33, where m = (1 − 3x/2). Maximum crystallite size was achieved by hydrothermal treatment between 180° and 200°C, with x = 0.337 to 0.429. Crystal strain was also minimized at these values of x. The adsorption capacity for Naphthol Yellow S increased as x increased and reached a maximum (1.56 × 10 −6 moles/m 2 ) when x = 0.287, a value eight times larger than that of Mg(OH) 2 . A weak endothermic DTA peak at about 350°C is probably due to the loss of structural water in the main layer of the structure. On calcination between 400° and 700°C, only periclase was detected, probably containing Al in solid solution. Hydration of the calcined product resulted in the reconstruction of the original hydrotalcite structure.