Collect. Czech. Chem. Commun. 2007, 72, 1284-1294

Rehydration of Calcined Mg-Al Hydrotalcite in Acidified Chloride-Containing Aqueous Solution

Bruno Kosturaa,*, František Kovandab, Marta Valáškováa and Juraj Leškoa

a Technical University Ostrava, 17. listopadu 15/2172, 708 33 Ostrava-Poruba, Czech Republic
b Department of Solid State Chemistry, Institute of Chemical Technology, Prague, Technická 5, 166 28 Prague 6, Czech Republic


The rehydration of periclase-like Mg-Al mixed oxide obtained by calcination of hydrotalcite- like precursor with a Mg/Al molar ratio of 2 was carried out in KCl-HCl solutions at various pH and constant concentration of Cl-. A buffer equilibrium accompanied by leaching out of Mg2+ cations from the solid was observed during rehydration, when reconstruction of the layered hydrotalcite structure takes place. With increasing HCl concentration in the rehydration solution, the Mg/Al molar ratio in the obtained solid gradually decreased from about 1.5 to 0.3. An anomaly was found, when the increasing concentration of acid resulted in increasing pH of final solution. The XRD measurements showed that the initially formed hydroxide form of hydrotalcite is transformed into randomly interstratified forms of the Mg-Al hydroxide hydrate/Mg-Al chloride hydroxide hydrate, which are accompanied by the release of OH- anions into solution. The crystalline structure of rehydrated product decreased as Mg2+ cations were released into solution, which was accompanied by incorporation of Cl- into the solid.

Keywords: Hydrotalcite; Layered double hydroxide; Magnesium; Aluminum; X-ray powder diffraction; Rehydration-reconstruction process.

References: 20 live references.