Uptake of benzenecarboxylate ions by magnesium aluminium oxides

The behaviour of uptake of the benzenecarboxylate ions, C₆H_6-n(COO)_nⁿ (n = 1–6), in aqueous solutions by rock-salt type magnesium aluminium oxide, Mg_(1-x)(2+x)Al_2x/(2+x)O (x = 0.17, 0.30, 0.33) was investigated at 0.70°C. All the benzenecarboxylate ions were taken up from solution competitively with OH- to form the hydrotalcite-like layered double hydroxides. The uptake rate could be adequately described by a surface chemical reaction controlled shrinking core model, and the apparent activation energy was c. 60 kJ mol^?1. The selectivity of anion uptake increased with increasing the charge density of the benzenecarboxylate ions. The amount of benzenecarboxylate ions incorporated in the interlayer of hydrotalcite and the selectivity of uptake for benzenecarboxylate possessing higher electric change increased with increasing aluminium content in the magnesium aluminium oxide.