PHASE-TRANSITION OF CL--INTERCALATED HYDROTALCITE-LIKE COMPOUND DURING ION-EXCHANGE WITH PHOSPHATES

A Cl--intercalated hydrotalcite-like compound (HTAL) was prepared by n eutralizing magnesium and aluminum chlorides with sodium hydroxide. Th e phosphate/Cl- ion exchange on HTAL was studied by X-ray diffraction (XRD), differential thermal (DTA)-thermogravimetry (TG) analyses, and nitrogen adsorption-desorption at 77 K. The process of phosphate/Cl- i on exchange could be divided into three stages depending on the amount (P(load)) of phosphate loading. In stage I (0% < P(load) < 6%), the C l--intercalated phase (interlayer distance = 0.30 nm) alone was observ ed. In stage II (6% < P(load) < 80%), the phase transition from the Cl --intercalated phase to the phosphate-exchanged phase (interlayer dist ance = 0.36 run) took place. In stage III (80% < P(load) < 100%), the phosphate-exchanged phase alone was observed; the interlayer distance increased slightly (from 0.36 to 0.37 nm) with an increase in the phos phate loading, indicating a formation of solid solution. DTA-TG analys es showed the presence of three kinds of water (surface, interlayer, a nd structural water) in the phosphate-loaded HTAL. The amount of surfa ce and interlayer water increased with an increase in the phosphate lo ading. Nitrogen adsorption study showed relatively small surface areas and pore volumes for the original HTAL (50 m2/g and 0.15 cm3/g) and p hosphate-loaded HTAL (49 m2/g and 0.10 CM3/g). This suggested that nit rogen molecules could not enter the interlayer space and were adsorbed on the surface of the microcrystals. A schematic model was proposed f or the phosphate/Cl- ion exchange on HTAL.