Ionic Strength-Induced Formation of Smectite Quasicrystals Enhances Nitroaromatic Compound Sorption

Hui Li,*† Tanya R. Pereira,† Brian J. Teppen,† David A. Laird,‡ Cliff T. Johnston,§ and Stephen A. Boyd†
Department of Crop and Soil Sciences, Michigan State University, East Lansing, Michigan 48824, National Soil Tilth Laboratory, USDA-ARS, Ames, Iowa 50011, and Crop, Soil, and Environmental Sciences, Department of Agronomy, Purdue University, West Lafayette, Indiana 47907
Environ. Sci. Technol., 2007, 41 (4), pp 1251–1256
DOI: 10.1021/es062274d
Publication Date (Web): January 9, 2007
Copyright © 2007 American Chemical Society
*

 Corresponding author phone:  (517)355-0271 ext 1146; fax: (517)355-0270; e-mail:  lihui@msu.edu.

†

 Michigan State University.

‡

 USDA-ARS.

§

 Purdue University.

Abstract

Sorption of organic contaminants by soils is a determinant controlling their transport and fate in the environment. The influence of ionic strength on nitroaromatic compound sorption by K+- and Ca2+-saturated smectite was examined. Sorption of 1,3-dinitrobenzene by K-smectite increased as KCl ionic strength increased from 0.01 to 0.30 M. In contrast, sorption by Ca-smectite at CaCl2 ionic strengths of 0.015 and 0.15 M remained essentially the same. The “salting-out” effect on the decrease of 1,3-dinitrobenzene aqueous solubility within this ionic strength range was <1.5% relative to the solubility in pure water. This decrease of solubility is insufficient to account for the observed increase of sorption by K-smectite with increasing KCl ionic strength. X-ray diffraction patterns and light absorbance of K-clay suspensions indicated the aggregation of clay particles and the formation of quasicrystal structures as KCl ionic strength increased. Sorption enhancement is attributed to the formation of better-ordered K-clay quasicrystals with reduced interlayer distances rather than to the salting-out effect. Dehydration of 1,3-dinitrobenzene is apparently a significant driving force for sorption, and we show for the first time that sorption of small, planar, neutral organic molecules, namely, 1,3-dinitrobenzene, causes previously expanded clay interlayers to dehydrate and collapse in aqueous suspension.

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History

  • Published In Issue February 15, 2007
  • Received for review September 23, 2006
    Revised manuscript received November 22, 2006
    Accepted November 27, 2006

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