A Thermodynamic Study of Interactions of Monoionic Kaolinite with N,N-Dimethylacetamide (DMA) and Pyridine (PY)

Two series of monoionic (M) kaolinites (M = H(+), Ca(2+), Cu(2+), Zn(2+), Al(3+), and Fe(3+)) were prepared from a natural Brazilian clay (São Simão clay, SP): series A, dried under vacuum at 25 degrees C, and series B, dried under vacuum at 25 degrees C. The natural clay was characterized by elemental analysis, cation exchange capacity, X-ray diffractometry, differential thermal analysis, and surface area measurements (BET). The interactions of M,M-dimethylacetamide and pyridine with these (M) kaolinites were studied by adsorption isotherms, titration calorimetry, and infrared spectroscopy (for pyridine only). The results indicated a coordinative interaction between M,M-dimethylacetamide and (M) kaolinites. For the interactions between pyridine and (M) kaolinites, the formation of hydrogen bonds (M = Al(3+), Fe(3+)), hydrogen and coordinative bonds (M = Cu(2+), Zn(2+)), and ionic pairs (M = H(+), Ca(2+)) was observed. For the pyridine-(Cu) kaolinite system, a substitution of water coordinated to Cu(2+) by pyridine was established.