The Nature of Laponite: Pure Hectorite or a Mixture of Different Trioctahedral Phases?

Abstract

A series of laponites and synthetic OH- and fluorinated hectorites prepared from hydrothermal and melting experiments at both industrial and laboratory scale were examined with XRD and FTIR (MIR and NIR) to determine their mineralogical composition and possible compositional heterogeneity. The end materials contained both Li- and Na-bearing phases. The industrial hydrothermal OH-smectites prepared at low temperatures consist of random mixed layer hectorite-stevensite-kerolite with about 40–50% hectorite layers, the remaining being stevensite and kerolite at roughly equal proportions. The FTIR spectra of these smectites contain, besides the main Mg3OH stretching/overtone bands at 3695–3690 and 7225–7214 cm−1, respectively, additional OH overtone bands at ~3716 and 7265 cm−1 (hydrated state). These bands might be linked to Mg2LiOH stretching modes. The melt-derived smectites are kerolite-free but still contain stevensite layers, although the preparation methods involved heating in the excess of 1000 °C. In these smectites Li might be partitioned to both octahedral and interlayer sites. Subsequent annealing of the melt-derived Mg-Li smectites caused migration of the exchangeable Li to the vacant octahedral due to the Hofmann-Klemen effect and thus decrease of the layer charge, as was indicated by the νO-D method. Hydrothermal synthesis of Mg-Li smectites at high temperature (400 °C) and pressure (1 kbar), yielded pure hectorite without stevensite or kerolite domains.

Hydration of Na-saturated synthetic stevensite, a peculiar trioctahedral smectite

“…The origin of the contrasting swelling behaviour observed for hectorite depending on its octahedral composition remains unexplained, but argues for additional investigation to assess the validity of the identification criterion proposed by Christidis & Koutsopoulou (2013) for contrasting compositions of the hectorite octahedral sheet. In particular, it is necessary to assess the influence of the following: (1) crystallinity on smectite hydration behaviour; (2) the octahedral composition on the hectorite ability to re-expand upon heating and EG solvation; and (3) the possible layer heterogeneity resulting from the presence of stevensite- and talc-like domains/layers in synthetic smectites (Christidis et al , 2018).

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“…heating and EG solvation; and (3) the possible layer heterogeneity resulting from the presence of stevensite-and talc-like domains/ layers in synthetic smectites (Christidis et al, 2018).…”

Hybrid Pigments from Anthocyanin Analogues and Synthetic Clay Minerals

“…Its composition, characterization, and properties also have been described. 55 , 56 Hydrochloric acid (HCl, Vetec) was used as received. Ultrapure water was used for the preparation of all aqueous solutions.…”

Clay nanolayer encapsulation, evolving from origins of life to future technologies

“…Most natural clay particles are typically of size 1 micrometer or less, composed of a stacked nanolayered type structure as drawn in Figure 3, with typically 100 layers or less in each stack [13,14]. Thus, clay two-dimensional layers come in different lateral diameters ranging from about 20 nanometers (Laponite [15] synthetic clay) via micrometers for natural montmorillonites all the way up to millimeters for natural vermiculites (Fig. 4b).…”