Thermal analysis of hydrotalcite synthesised from aluminate solutions

The aluminate hydrotalcites are proposed to have either of the following formulas: Mg4Al2(OH)(12)(CO3 (2-))center dot xH(2)O or Mg4Al2(OH)(12)(CO3 (2-), SO4 (2-))center dot xH(2)O. A pure hydrotalcite phase forms when magnesium chloride and aluminate solutions are mixed at a 1:1 volumetric ratio at pH 14. The synthesis of the aluminate hydrotalcites using seawater results in the formation of an impurity phase bayerite. Two decomposition steps have been identified for the aluminate hydrotalcites: (1) removal of interlayer water (230 A degrees C) and (2) simultaneous dehydroxylation and decarbonation (330 A degrees C). The dehydration of bayerite was observed at 250 A degrees C. X-ray diffraction techniques determined that the synthesis of aluminate hydrotalcite with seawater and a volumetric ratio of 4.5 results in very disordered structures. This was shown by a reduction in the mass loss associated with the removal of interlayer water due to the reduction of interlayer sites caused by the misalignment of the metal-hydroxyl layers.