Effects of Pulverization and Heat Treatment for Phosphorous Removing Ability of Hydrotalcites

Hydrotalcite like material is an inorganic one having a layered double hydroxide structure (LDH) and one of promising materials for the use of various anion exchangers.In this study, the effects of milling and calcination conditions were investigated on the removal efficiencies of phosphorous of the CO32--hydrotalcite.Commercial CO32--hydrotalcite was milled with a vibrating ball mill under dry condition and followed by calcinations at various temperatures from 200 to 800°C. For un-ground hydrotalcite, calcination at 500°C led to the highest removal efficiencies of phosphorous. On the other hand, the hydrotalcite dry-milled with a vibrating ball mill for 24h showed the highest removal efficiencies of phosphorous on calcining at 200°C. The phosphorous removal by the hydrotalcite calcined at 500°C probably proceeds due to the rehydration of oxide phase, which is precipitated during calcination, accompanied with the re-structure of LDH and intercalation of phosphoric ions. For the hydrotalcite dry-milled and calcined at 200°C, the LDH structure still remains but almost all interlayer water is eliminated during milling and calcining. Therefore, phosphoric ion seems to be easily intercalated into interlayer space between host hydroxide layers. From these results, it is suggested that dry-milling with a vibrating ball mill is effective to reduce calcination temperature for the improvement in the removal ability of phosphorous of CO32--hydrotalcite.