Interpretation of the infrared NH4+ spectrum of the NH4+-clays: application to the evaluation of the layer charge

The IR spectra of NH4+-saturated smectites were examined in terms of their charge characteristics. The upsilon 4 NH4+ band near 1440 cm(-1), observed in the DRIFTS spectra (obtained without use of a KBr matrix), was assigned to the vibrations of NH4+ ions compensating the negative charge of the clay s. When KBr was used as a diluting matrix, the upsilon 4 NH: band was locat ed at 1400 and/or 1440 cm(-1). The band at 1400 cm(-1), related to NH4Br, o riginated from the replacement of NH; in the clay by K+ from the KBr. For s welling clay minerals this band indicates that layers have permanent low ch arge density and/or variable charge. For non-swelling clay minerals, the 14 00 cm(-1) band characterizes the presence of variable charges only. The u4 NH4+: band at 1440 cm(-1) suggests that NH4+ in the clay was not replaced b y K+ from KBr and remains in the interlayer space of the clay minerals. Thi s absorption is due to NH4+ compensating only permanent charge in the inter layers, or part of the interlayers with a high charge density. The presence of both bands at 1400 cm(-1) and 1440 cm(-1) in the IR spectrum suggests t hat the clays studied have a heterogeneous interlayer charge.