Deintercalation of Carbonate Ions from a Hydrotalcite -Like Compound: Enhanced Decarbonation Using Acid-Salt Mixed Solution

Because of the high affinity of the carbonate ion (CO32-) to the hydrotalcite-like compounds or LDHs (layered double hydroxides), it was difficult to deintercalate carbonate ions and convert them into other LDHs with an easier anion-exchangeability. By treatment with dilute acids such as HCl, the conversion is limited, and, at higher concentrations, changes in shape and weight loss occurred. We found that the addition of NaCl dramatically enhanced the deintercalation of carbonate ions by dilute HCl solution (0.0025-0.005 N). It made the carbonate ions very rapidly deintercalate from the hydrotalcite-like compounds at 25 C without any weight loss. Scanning electron microscopy (SEM) revealed that no morphological change occurred. Furthermore, by changing the HCl/NaCl ratio, it was possible to regulate the exchange ratio. Protonation of carbonate ions in the interlayer space and successive ion exchange with a large excess of Cl- ions was assumed to be the mechanism for this enhanced deintercalation.