Adsorption of ABS on Soil Minerals
COOPER H. WAYMAN, Research Engineer
JOHN B. ROBERTSON, Hydraulic Engineer
U. S. Geological Survey
Denver, Colorado
INTRODUCTION
When household or sewage waste water containing incompletely degradable
surfactants in detergents infiltrates into the ground from rivers, streams, cesspools, or septic tanks, pollution of ground water may occur. Because clay minerals possess large surface areas and also comprise significant amounts of major
soil types, clay minerals were considered to be a potential source of natural material for the removal of the surfactant, alkalybenzenesulfonate(ABS), from infiltrating waste water. In waste water ABS consists of various proportions of a
branched-chain ion ranging from 12 to 15 carbon atoms and may be represented
as
[R-C6H4-S03]
-1
where R represents an alkyl chain.    In this study R contained either 12 carbon
atoms (dodecyl ABS) or 15 carbon atoms (pentadecyl ABS).
A radiochemical tracer technique was combined with membrane dialysis to
study the effects of varying ABS concentration, alkyl chain length, pH, the additives phosphate and carboxymethylcellulose ions, and salt content (NaCl,
CaCl2, or AICI3) on ABS adsorption by the clay minerals (kaohnite, illite, and
montmorillonite). The adsorption data for clays are compared to those obtained
for synthetic adsorbents, activated charcoal, and "Baymal" (colloidal alumina).
EXPERIMENTAL PROCEDURE
The clay samples employed in the study were kaolinite (Dry Branch, Georgia), illite (American Petroleum Institute No. 35, Fithian, Illinois), and montmorillonite (American Petroleum Institute No. 26, Clay Spur, Wyoming). All
clays were used without treatment other than sizing at two microns with "Calgon"
[NaP03)g] as the dispersant; additional sizing was carried out with an ultracen-
trifuge   producing clay in the size range 0.2 to 2.0 microns.
The experimental set-up is shown in Figure 1. In each experiment 10 ml of
a clay suspension at a concentration of 200 mg per 10 ml of deionized-distilled
water were sealed in a sausage casing (membrane tube) and placed in a small
polyethylene bottle. Ten ml of a radioactive ABS 35 (either dodecyl or pentadecyl at an original specific activity of one millicurie per millimole) solution of
different concentrations with or without other anions and cations were then pipetted into the bottle around the clay (external to the sausage casing) and the
capped bottle was placed in a constant temperature (25 ± 1 C) agitated water
bath. The total volume of the liquid phase was 20 ml and the total weight of the
clay was 200 mg. The casing functioned as a molecular sieve, being permeable
to ABS ions but impermeable to clay particles. In time various amounts of ABS
would equilibrate with the clay surface.
The solutions were sampled in duplicate one-ml aliquots and evaporated to
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