The synthesis and spectroscopic characterisation of hydrotalcite formed from aluminate solutions

Raman spectroscopy has been used to characterise nine hydrotalcites prepared from aluminate and magnesium solutions (magnesium chloride and seawater). The aluminate hydrotalcites are proposed to have the following formula Mg6Al2(OH)16(CO32−)·xH2O, Mg6Al2(OH)16(CO32−,SO42−)·xH2O, and Mg6Al2(OH)16(SO42−)·xH2O. The synthesis of these hydrotalcites using seawater results in the intercalation of sulfate anions into the hydrotalcite interlayer. The spectra have been used to assess the molecular assembly of the cations and anions in the hydrotalcite structures. The spectra have been conveniently subdivided into spectral features based upon the carbonate anion, the hydroxyl units and water units. This investigation has shown the ideal conditions to form hydrotalcite from aluminate solutions is at pH 14 using a magnesium chloride solution at a volumetric ratio of 1:1. Changes in synthesis conditions resulted in the formation of impurity products aragonite, thenardite, and gypsum.

. Raman spectroscopy has been used to characterise nine hydrotalcites prepared from aluminate and magnesium solutions (magnesium chloride and seawater). The aluminate hydrotalcites are proposed to have the following formula Mg6Al2(OH)16(CO32−)·xH2O, Mg6Al2(OH)16(CO32−,SO42−)·xH2O, and Mg6Al2(OH)16(SO42−)·xH2O. The spectra have been used to assess the molecular assembly of the cations and anions in the hydrotalcite structures.Figure optionsDownload as PowerPoint slideHighlights
► Hydrotalcite was synthesised using Bayer refinery liquors.
► Aluminate hydrotalcites have the following formula Mg6Al2(OH)16(CO32−,SO42−)·xH2O.
► Coordination characteristics of water, carbonate and sulfate anions have been identified.
► No impurities were found for synthesis conditions: MgCl2·6H2O, pH 14, and volumetric ratio of 1:1.