FTIR STUDY OF DEUTERATED MONTMORILLONITES: STRUCTURAL FEATURES RELEVANT TO PILLARED CLAY STABILITY

Abstract-- FTIR studies of six partially-deuterated montmorillonites (MS) reveal the presence of two O-D stretching bands, one between 2702-2728 cm ~ and another near 2680 cm- ~. For homoionic (Li, Na, Mg, Ca, or La) Wyoming-type MS, the position of the higher frequency band, designated as (O--O)h, is between 2714-2728 cm-t, whereas for homoionic Cheto-type MS it is between 2702-2706 cm-l. The lower frequency band, designated as (O-D)~, is in the narrow range of 2674-2684 cm ~. Resolution of two corresponding O-H bands, appearing near 3670 and 3635 cm-~, was observed only after partial dehydroxylation f the smectites. The changes in the relative intensities of the two O-D stretching bands as a function of the smectite type and of the Lewis acidity (charge density) of the exchangeable ion were determined. For Wyoming-type MS, the intensity of the (O-D)h band is much lower than that of the (O-D)t band, whereas for Cheto-type MS, the intensity of the (O-D)h band is about equal or slightly higher than that of the (O-D)z band. The observed resolution can be ascribed tentatively to the presence of (at least) two types of octahedral OH groups in the smectites, the (O-D)h band being assigned to A1MgOH and the (O-D) ~ band to A1A1OH groups. Pillaring of Cheto-type MS with hydroxy-Al~3 oligocations resulted in products howing much higher thermal stability between 400-600 ~ compared to that of identically pillared Wyoming-type MS. Compositional nd other factors, e.g., CEC values and mode of pillaring, may cause this difference in stability. Key Words--Deuterated montmorillonites, FITR, Pillared smectites, Thermal stability