Acid Treatment of Layered Double Hydroxides Containing Carbonate

Carbonate-containing Mg-Al layered double hydroxides (LDHs) with two different crystallinities were treated with acidic solutions that contain Cl-. Upon treatment with an acetate buffer/NaCl aqueous solution, low-crystallinity LDH consumed more protons for dissolution of the metal hydroxide layers than did high-crystallinity LDH, and it showed a lower extent of exchange of interlayer anions for Cl- than high-crystallinity LDH. Varying washing procedures also resulted in differences in the characteristics of the washed products, such as the presence of Al(OH)(3) and the extent of exchange for Cl-. When chloride-containing LDHs were dispersed in water, Mg hydroxide species in the LDHs were found to be dissolved to some extent even in water, and Cl- ions in the LDHs were replaced with OH-ions that were formed by the dissolution.