The precipitate formed during the seawater neutralization (SWN) of Bayer liquors has been characterized by a variety of techniques, including X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma optical emission spectroscopy (ICP-OES), infrared and Raman spectroscopy, and thermal analysis. Three mineralogical phases are detected: (1) hydrotalcite, (2) calcite (CaCO3), and (3) aragonite (CaCO3). It is proposed that two hydrotalcite structures form and have the formulas Mg8Al2(OH)(12) (CO32-,SO42-)center dot xH(2)O and Mg6Al2(OH)(16)(CO32-,SO42-)center dot xH(2)O. The Mg, Al molar ratio of the Bayer hydrotalcite is dependent on both the pH and the composition of the initial Bayer liquor. It is proposed that carbonate and sulfate ions are intercalated predominantly into the hydrotalcite interlayer; however, small amounts of arsenate, vanadate, and molybdate have been shown to be removed from solution. The formation of Bayer hydrotalcite assists in the removal of oxy-anions of transition metals from bauxite refinery residues, through a combination of intercalation and adsorption reactions involving the newly formed hydrotalcite. Infrared and Raman spectroscopy also confirmed the presence of hydrotalcite, calcite, and aragonite, showing characteristic wavenumbers of hydroxyl stretching modes for hydrotalcite, and antisymmetric stretching modes of carbonate for the calcium carbonate minerals. ICP-OES also confirmed the removal of oxy-anions from Bayer liquors.