Intercalation of smectite with liquid ethylene glycol — Resolved in time and space by synchrotron X-ray diffraction

Using synchrotron X-ray powder diffraction we studied the reaction of liquid ethylene glycol and smectite, i.e. (i) the time-resolved glycolation of Mg-smectite (Georgian Ibeco Seal M-90) films equilibrated to form hydrates with 0–3 water layers, and (ii) time and spatially resolved glycolation of homoionic Li-, Na-, K-, Mg-, and Ca-montmorillonite powders (Wyoming MX80) equilibrated to ambient atmosphere and packed in glass capillaries.The films in (i) were approximately 65 μm thick and complete reaction was achieved within minutes. The relative intensity of the 17 Å-smectite-glycolate varied linearly with the square root of time and the effective diffusion coefficients were determined to be of the order of 10–11 m2/s. In the one-layer hydrate experiment the basal spacing increased from 12.5 to 14.5 Å during the reaction, which indicated a redistribution of water in the sample.The capillaries in (ii) were 1.5 mm in diameter and were investigated along their length using a 1 × 1 mm X-ray beam. The wet part contained the 17 Å-montmorillonite-glycolate in all cases. In the dry part, close to the wetting front, a 0.5–2 mm zone with increased basal spacing was observed in all cases, except for the K-form. The zone with increased hydration contained: more two-layer-hydrate (Li, Na), four-layer-hydrate (Mg) and three-layer-hydrate (Mg, Ca). Further from the liquid the montmorillonite was present in its original hydration state as one-layer-hydrate (Li, Na, K) or two-layer-hydrate (Mg, Ca). The transport of liquid glycol into the montmorillonite in the tube was thus coupled to a transport of water on the mm-scale.