Organic Sorption from Aqueous
Solution by Two Clays
MING-DEAN LUH, Fellow
ROBERT A. BAKER, Senior Fellow
Mellon Institute
Carnegie-Mellon University
Pittsburgh, Pennsylvania
INTRODUCTION
Despite the universal distribution of clay minerals in natural waters, relatively
little is known about the sorption or organic contaminants from aqueous solution
onto these clays. Organic-clay systems are important in water technology. Clays of
colloidal dimensions may act as condensation nuclei for organics and facilitate their
transport. The particulates of smallest size and possessed of high electronegative
charge often escape coagulation basins of water treatment plants (1). If organic
species are sorbed onto these particles which carry over into the treated water they
pose a potential source of quality impairment. This research is a direct outgrowth of
interest in the effect such organic-clay systems may have on taste and odor of water.
It was necessary to first characterize the nature and extent of sorption of selected
clay-organic systems with particular emphasis on dilute aqueous systems. The
primary objective of this study was to examine the sorptive properties of two homo-
ionic clays, a sodium kaolinite and a sodium montmorillonite, toward commonly-
occurring organic acid contaminants such as phenol and substituted phenol. Special
experimental techniques had to be developed because of the instability of organic-
clay systems at Mg/1 to mg/1 concentrations. This paper describes the techniques
evolved and presents the results of preliminary sorption studies.
EXPERIMENTAL
Sodium montmorillonite and sodium kaolinite which were highly purified and
made homoionic by previously described techniques (2) were the clays studies.
Cation exchange capacities are 115.1 and 16.6 meq/100 gm and specific surface areas
are 78.2 and 21.3 sq m/gm respectively. The kaolinite mean particle diameter is 0.2^
with 96 per cent <0.6/x. The montmorillonite is not amenable to electron microscopic sizing but particle size is assumed to be in a comparable range because of the
similarity in method of preparation and size separation. Phenol, m-cresol, 2,4
dichlorophenol, m-aminophenol, 2,4 diaminophenol hydrochloride and sodium salts
of valeric and n-hexanoic acids were the organic compounds studied. C-14 tagged
organic compounds were obtained from Amersham/Searle Corporation, Des Plaines,
Illinois.
All glassware, dilution water, clay suspensions and chemical stock solutions
were sterilized. Sterile techniques were practiced in sample preparation. Solutions
were prepared in two oz, serum-stoppered bottles. The stoppers were boiled for two
hr and then rinsed with sterilized, deionized water prior to use. A 38 ml volume of
solution containing the organic chemical was first added to the sample bottle. A two
per cent suspension of clay was prepared separately. These solutions and all blank
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