Research paper
Cyclic carbonate–sodium smectite intercalates

https://doi.org/10.1016/j.clay.2016.02.005Get rights and content

Highlights

  • Cylcic carbate solvents are of interest for improving saline resistance of bentonites.

  • Various cyclic carbonate can be derived from glycerol carbonate.

  • Intercalates of glycerol carbonate and some of its derivatives with Mt were studied.

  • XRD and IR results indicated strong interactions between intercalate and Mt interlayers.

  • Stable and highly ordered glycerol carbonate–Mt complex formed at 1:1 ratios.

Abstract

Five-membered cyclic organic carbonates (COC) are of interest for their ability to modify the surface properties of smectites and enhance the hydraulic resistance of bentonites to saline leachates. The mechanism of interaction of glycerol carbonate (GC) and several other hydroxyl containing cyclic organic carbonates (generally having progressively greater molecular masses) with sodium montmorillonite (Na+-Mt) was studied using powder X-ray diffraction and infrared spectroscopy. The 001 reflection for GC/Na+-Mt intercalates varied with the amount COC added, and the measured d001 value increased from 1.29 nm to as large as 2.22 nm at equal-mass coverage of the COC to Na+-Mt. In general, when intercalated, the cyclic carbonyl (Cdouble bondO) stretch and the fundamental hydroxyl (O–H) stretch bands of COC derivatives were red-shifted with respect to these bands for neat COC, indicating strong ion-dipole interaction of the carbonyl group with interlayer Na+, and H-bonding of the OH group with both interlayer water and Mt surfaces. A stable and highly ordered intercalate was produced at a 1:1 mass loading with Mt in which about 6 GC molecules per unit cell (~ 7 molecules per Na+ ion) replaced most of the interlayer water.

Introduction

A high swell capacity and low saturated hydraulic conductivity make sodium bentonite useful as a component in geosynthetic clay liners (GCL) (Eglofgstein, 2001, Bouazza, 2002 Gates et al., 2009). However, bentonites undergo significant increases in saturated hydraulic conductivity when exposed to saline leachates arising from osmotically induced desiccation and associated changes in texture (Quirk and Schoffield, 1955, Guyonnet et al., 2005), thereby enabling these leachates to potentially contaminate underlying sediments and groundwater. GCL performance is thus often limited by the ability of the bentonite component to swell and form and maintain strong gels (Bouazza and Gates, 2014).

Various types of modifications have been developed to improve the chemical and functional capabilities of bentonite, ranging from doping with soda-ash (Harvey and Lagaly, 2006), the addition of polymers (Theng, 2012) to modifying with organo-surfactants (Yang and Lo, 2004) or with solvents (Onikata, 1999), and some of these methodologies have been applied to GCLs (Eglofgstein, 2001, Katsumi et al., 2008, Scalia et al., 2014).

In particular, five-membered cyclic organic carbonate (COC), a class of polar aprotic solvents, have been shown to have unique properties such as high polarity and a propensity for coordinating with metal cations via cation-dipole interactions (Yamanaka et al., 1974, Chernyak, 2006). In addition to high solvency, COC molecules also possess low flammability, high boiling and flash points, low odour levels, low vapour pressure (Verevkin et al., 2008) and generally low toxicities (Anonymous, 1987). Propylene carbonate (PC) forms intercalation complexes with montmorillonite (Mt) that have been found to enhance the swelling of Mt in brines (Onikata and Kamon, 1996, Onikata, 1999), a phenomenon exploited in the ‘multiswellable’ bentonite products (Onikata et al., 1999, Katsumi et al., 2008). Unlike sodium bentonite, PC-modified bentonite retains good swelling in up to 0.3 M CaCl2 (Onikata, 2002) and is currently proposed as an alternative material for liner systems (Katsumi et al., 2008).

Glycerol carbonate (GC) and several of its COC derivatives, were catalytically synthesized from urea and 1,2-diols employing zinc monoglycerolate as a catalyst (Turney et al., 2013). Preparations of cyclic carbonate intercalates of Na+-Mt were made (see Supplementary information) to study the mechanisms by which the composite materials maintained a swollen state in high ionic strength leachates, with the aim to develop new materials for application in clay barriers against high levels of salinity. This study details the results from X-ray diffraction and infrared spectroscopic study of the structures and properties of the intercalates.

Section snippets

Materials & methods

Sodium-bentonite, supplied from Sibelco Pty. Ltd. (Melbourne) is mined near Miles, Queensland and has well known and consistent mineralogy. The < 0.2 μm fraction of 25 g of bentonite (containing > 98% smectite, Table 1) was separated by sedimentation and centrifugation following general procedures (Gates et al., 2002). The fine fraction was rinsed three times with ~ 2 M NaCl, washed and dialyzed to remove excess salts and freeze-dried to a powder. Approximately 13 g of < 0.2 μm Na+-Mt was prepared from

Interaction of GC with Na+-Mt

To determine the appropriate load rates of GC and its derivatives for modifying Na+-smectite, the XRD traces of GC/Na+-Mt intercalates were measured as a function of percent mass coverage (Fig. 1A). A d001 value of 1.29 nm was observed for the 001 reflection of the air-dried Na+-Mt, indicating mostly a 1-layer hydrate. On loading with GC, the d001 value generally increased from ≈ 1.40 nm (9% coverage) to 3.7 nm (900% coverage). For the coverage from 35 to 67%, two d001 values were apparent, one near

Conclusions

Various wt% of glycerol carbonate were mixed with Na+-Mt to probe the resulting GC/Na+-Mt intercalates using XRD and FTIR. An ordered complex was obtained with a 100 wt% GC load rate, whereas greater GC loadings resulted in considerable interlayer disorder. The observed interlayer space for intercalates of the more complex COC derivatives with Na+-Mt increased logically with molecular dimensions of the COC, but the functional moiety also impacted on the resulting d-value.

The main driving force

Author contributions

WPG, TWT and AFP conceptualized and developed the research project and secured Australian Research Council financial support (ARC DP1095129). US conducted the research presented herein as part of the requirements leading to a PhD.

Author information

The authors declare no financial interests.

Acknowledgements

This work was financially supported by Australian Research Council's Discovery Projects Scheme (grant no.: DP1095129). U. Shaheen gratefully acknowledges receipt of a fees remission scholarship and Postgraduate Publication Award from the Faculty of Science. The authors also thank Sanji Kulasegaram, Sally Duck and Craig Forsyth from Monash University for laboratory and instrumental support.

References (36)

  • BujdákJ. et al.

    Molecular orientation of rhodamine dyes on surfaces of layered silicates

    J. Phys. Chem. B

    (2006)
  • ChernyakY.

    Dielectric constant, dipole moment, and solubility parameters of some cyclic acid esters

    J. Chem. Eng. Data

    (2006)
  • S.C.T. Deeds et al.

    Density studies in clay-liquid systems

    II. Application to core analysis. Proc. Natl. Conf. Clays Clay Miner.

    (1963)
  • EglofgsteinT.A.

    Natural bentonites – influence of the ion exchange and partial desiccation used on permeability and self-healing of bentonites used in GCLs

    Geotext. Geomembr.

    (2001)
  • FedorsR.F.

    A method for estimating both the solubility parameters and molar volumes of liquids

    Polym. Eng. Sci.

    (1974)
  • FehervariA. et al.

    Organicially modified bentonites as effective hydraulic barriers to hypersaline leachates

    Geotext. Geomembr.

    (2015)
  • GatesW.P. et al.

    Bentonite clay keeps pollutants at bay

    Elements

    (2009)
  • GuyonnetD. et al.

    Geosynthetic clay liner interaction with leachate: correlation between permeability, microstructure, and surface chemistry

    J. Geotech. Geoenviron.

    (2005)
  • Cited by (0)

    View full text