Hydroxyl groups and water in palygorskite Available to Purchase

Infrared spectra of the coordinated water in palygorskite were studied at different degrees of exchange of deuterone and protons. The single peaks observed for the bending fundamental of isotopically diluted H₂O and D₂O show that all the coordinated water molecules are equivalent, as suggested by Bradley’s structure determination. The doublets observed for the three fundamentals of isotopically dilute HDO showed that the coordinated water molecules are asymmetric (C_s symmetry). Response of palygorskite films to the angle of orientation indicated one of the OH stretching modes to have its transition moment nearly perpendicular to the [100] plane. The orientation effect results from one of the protons on each of the coordinated water molecules forming a hydrogen bond directed towards the hexagonal holes of oxygens fprmed by the Si-O-Si connections between the amphibole chains, and it explains the distorted character of this water. Deuteration and orientation studies also verified that the two OH stretching bands of the distorted water are truly uncoupled.

Georgia palygorskite is shown to be completely dioctahedral, and a model is presented to explain its octahedral cation occupancy and the frequency of the structural hydroxyls. Infrared adsorption bands around 3700 cm^-1 indicated the presence of some SiOH groups in the mineral. These groups are less abundant in palygorskite than in sepiolite, indicating that palygorskite has less exposed edges.