Interpretation of the infrared spectrum of the -clays: application to the evaluation of the layer charge

The IR spectra of -saturated smectites were examined in terms of their charge characteristics. The υ4 band near 1440 cm-1, observed in the DRIFTS spectra (obtained without use of a KBr matrix), was assigned to the vibrations of ions compensating the negative charge of the clays. When KBr was used as a diluting matrix, the υ4 band was located at 1400 and/or 1440 cm-1. The band at 1400 cm-1, related to NH4Br, originated from the replacement of in the clay by K+from the KBr. For swelling clay minerals this band indicates that layers have permanent low charge density and/or variable charge. For non-swelling clay minerals, the 1400 cm-1band characterizes the presence of variable charges only. The υ4 band at 1440 cm-1suggests that in the clay was not replaced by K+from KBr and remains in the interlayer space of the clay minerals. This absorption is due to compensating only permanent charge in the interlayers, or part of the interlayers with a high charge density. The presence of both bands at 1400 cm-1and 1440 cm-1in the IR spectrum suggests that the clays studied have a heterogeneous interlayer charge.