Effect of Rehydration Conditions on the Physicochemical Properties of Reduced Layered Double Hydroxides of Magnesium and Aluminum

Using the method of solid-phase reaction of AlCl₃·6H₂O and MgCl₂·6H₂O with (NH₄)₂CO₃ at room temperature, a Mg–Al layered hydroxide with composition Mg₄Al₂(OH)₁₂CO₃·3.85H₂O with the structure of hydrotalcite is obtained. The results of determining the effect of rehydration conditions on the structural and surface properties of layered reduced double hydroxides (LDHs) of magnesium and aluminum are described. It is shown that the samples obtained by reduction of thermally treated initial Mg–Al LDH for 2 h (regardless of the pH of the medium) have specific surface-area parameters (both total area and outer surface area) that are not different from those of the initial LDH sample, and their specific pore volume increases by a factor of 1.3–1.5 (from 0.121 to 0.159–0.183 cm³/g). It is established that the pH of the isoionic point of the rehydrated Mg–Al LDH samples depends only slightly on the rehydration conditions and equals 9.7 ± 9%, which suggests a high sorption capacity of both synthesized and rehydrated Mg–Al LDH samples with respect to nonferrous metal ions.