HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Bailey, G. W. Articles by Rothberg, T. Search for Related Content PubMed Articles by Bailey, G. W. Articles by Rothberg, T. Agricola Articles by Bailey, G. W. Articles by Rothberg, T.

Adsorption of Organic Herbicides by Montmorillonite: Role of pH and Chemical Character of Adsorbate¹

ABSTRACT

Samples of well-characterized 1-0.2µ montmorillonite clay adjusted to two pH values, pH 3.35 and 6.80, were reacted with members of such herbicide families as s-triazines, substituted ureas, phenylcarbamates, aniline, anilides, phenylalkanoic acids, benzoic acids, and picolinic acids.

Graphical methods were used to plot adsorption isotherms and to determine conformity to the Freundlich or Langmuir equations. Calculations were made to determine: (i) the percent cation exchange capacity satisfied at the maximum amount adsorbed; (ii) the percent surface coverage at the maximum amount adsorbed; and (iii) the partial molar-free energy for each concentration level; also determined graphically was the Freundlich "K" and "1/n" value.

Conformity to the Freundlich adsorption equation was found for all organic compounds studied for both the H-clay and the Na-clay systems with two possible exceptions: the phenoxyacetic acid-H-clay system and the substituted urea-Na-Clay systems. Conformity to the Langmuir adsorption equation was not found for any family or group studied on either H- or the Na-saturated clay.

Regardless of chemical character, adsorption occurred to the greatest extent on the highly acid H-montmorillonite compared to the near neutral Na-montmorillonite.

Within a family or within an analog series basic in chemical character, the magnitude of adsorption is related to and governed by the degree of water solubility. The major factor governing the magnitude of adsorption of different basic chemical families is the dissociation constant of the adsorbate.

The magnitude of adsorption of organic compounds with widely different chemical character is governed by the degree of water solubility, the dissociation constant of the adsorbate, and the pH of the clay system.

The adsorption of basic organic compounds by the montmorillonite type clay system appears to be dependent upon surface acidity and not upon the pH of the suspension while the converse appears to hold true for the adsorption of acidic type compounds.

The surface acidity of montmorillonite appears to be 3–4 pH units lower than the suspension pH.

Mechanisms for the adsorption of basic and acidic organic compounds are discussed.

¹ Contribution of Agronomy Department, Purdue Agr. Exp. Sta., Purdue Univ., Lafayette, Ind., as Journal Article no. 3036. Presented before Div. S-3 Soil Science Society of America, Columbus, Ohio, Nov. 1, 1965. The research was supported by Division of Environmental Engineering & Food Protection, US Public Health Service Grant EF-00055. Publication supported by Public Health Service Research Grant CC-00248 from the National Communicable Disease Control Center, Atlanta, Georgia.

² Post Doctoral Research Associate, Professor of Agronomy, and Laboratory Technician, respectively. Present address of senior author is Southeast Water Laboratory, Athens, Georgia, Federal Water Pollution Control Admin., US Department of the Interior.

Received for publication May 22, 1967. Accepted for publication October 12, 1967.