Cation composition during recrystallization of layered double hydroxides from mixed (Mg, Al) oxides

Changes in cation composition and M2+/M3+ ratio during hydrotalcite regeneration were studied. Regenerated hydrotalcites were obtained by recrystallization of mixed (Mg, Al) oxides in solutions of divalent (Mg, Zn, Co, Ni, Cu) or trivalent (Al, Fe) cations. g Mg–Al–CO3 hydrotalcites with Mg/Al=2, 3 and 3.7, at 600 °C for 2 h yielded periclase-like mixed (Mg, Al) oxides (HT-P). The hydrotalcite structure was restored by dispersing oxides 48 h in water or aqueous solutions of different cations. esence of Mg2+, Zn2+, Ni2+, Co2+, Cu2+ salts or of low soluble hydromagnesite increased the M2+/Al ratio, reaching a maximum value of 3.8. An incorporation of Zn2+, Ni2+, Co2+ and Cu2+ cations in the newly formed hydrotalcite was detected, while Mg2+ remained in solution. In the presence of soluble Al salts or freshly precipitated Al(OH)3, the M2+/Al ratio approximated the minimal possible value of 2. /Al ratio of a hydrotalcite crystallized from a mixture of two HT-P samples with different Mg/Al ratios is equal to the weighted average value. sults obtained support the conception of the dissolution–crystallization mechanism of hydrotalcite regeneration from mixed (Mg, Al) oxides contrary to the widely accepted concept of topotactic processes.