HYDROTALCITE (Mg_6Al_2(OH)_(16)(CO_3).4H_2O): A POTENTIALLY USEFUL RAW MATERIAL FOR REFRACTORIES

摘要

Hydrotalcite also known as aluminum-magnesium layered double hydroxide (LDH), was broadly investigated in the past decade due to its many applications as catalyst support, adsorptive flotation and flame retardant in polymers. For these applications, it can be synthesized using coprecipitation of Al-Mg soluble salts. In refractories castables, hydrotalcite was firstly described as a byproduct of the hydroxylation reaction between magnesia sinter and hydratable alumina or calcium aluminate cement. In these cases, because only a small portion of hydrotalcite has been formed at the surface of the sinter particles, the deleterious effects of magnesia hydroxylation reaction were significantly minimized. Recently, using similar reactions, novel methodologies were developed to produce large quantities of hydrotalcite starting from caustic magnesia and aluminum hydroxide under controlled temperature and curing conditions. Considering its chemical composition (Mg_6Al_2(OH)_(16)(CO_3).4H_2O), which is roughly 60 wt.% MgO and 40 wt% Al_2O_3 and the many advances attained regarding its synthesis, hydrotalcite has a great potential to be used in refractories, especially those aiming the in situ generation of spinel (MgAl_2O_4). This paper reviews critically the many occurrences of hydrotalcite in refractories, the most effective synthesis methods and presents some potential uses of this raw material in refractory compositions.