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

Two series of monoionic (M) kaolinites (M= H+, Ca2+, Cu2+, Zn2+, Al3+, and Fe3+) were prepared from a natural Brazilian clay (São Simão clay, SP): series A, dried under vacuum at 25°C, and series B, dried under vacuum at 25°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 ofM,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 betweenM,M-dimethylacetamide and (M) kaolinites. For the interactions between pyridine and (M) kaolinites, the formation of hydrogen bonds (M= Al3+, Fe3+), hydrogen and coordinative bonds (M= Cu2+, Zn2+), and ionic pairs (M= H+, Ca2+) was observed. For the pyridine–(Cu) kaolinite system, a substitution of water coordinated to Cu2+by pyridine was established.