Hydrotalcite-like compounds: A way to recover a hazardous waste in the aluminium tertiary industry

Magnesium–aluminium hydrotalcite-like compounds at ratios of 2:1, 3:1 and 4:1 were prepared using a non-conventional aluminium source, the hazardous wastes from the aluminium tertiary industry. The method consisted in a conventional coprecipitation at constant pH 10 with magnesium chloride hexahydrate and stable solutions of Al3 + from dispersions of the fine powder from the sleeve filter suction system in the aluminium slag milling process. The characterisation of the resulting materials indicated that hydrotalcites were strongly dependent on the presence of iron in the layers, as well as the carbonate and chloride content in the interlayer which affected the final properties. XRD and SAED indicated low crystallinity for these materials. Furthermore, as can be seen by SEM, the formation of disordered tiny nuclei was significant causing small spherical agglomerates. The infrared spectra showed a change of symmetry in the interlayer for the different ratios and the textural data suggested the “ink-bottle shaped” mesopores and type IIb isotherms, similar to the results obtained for pillared clays, and the transition to H2 type in the hysteresis loops as a function of the higher ratio.