Anion intercalation and exchange in Al(OH)3-derived compounds

Precipitation of Al³⁺ at pH = 10 in excess Li₂CO₃ leads to an anion exchanging compound, Al₂Li(OH)₆]⁺₂CO²⁻₃. This compound exhibits, compared to Mg₃Al(OH)₈]⁺₂CO²⁻₃, a higher degree of size selectivity in anion exchange. The structure of the Al₂Li(OH)₆]⁺ layers is gibbsite-like, with a (110) diffraction feature at d = 4.35 Å indicating a pronounced Al³⁺ ordering. As claimed originally by Serna et al., the structure is Al₂Li(OH)₆]⁺A^z−_1/z rather than Al₂(OH)₆]Li⁺A^z−_1/z, with the Li⁺ coordinated in the octahedral positions left vacant by Al³⁺. This emerges from the details of a lithium-leaching process, which proposedly leads to a novel compound, Al₂H(OH)₆]⁺A^z−_1/z.