Ku. Goss, EFFECTS OF TEMPERATURE AND RELATIVE-HUMIDITY ON THE SORPTION OF ORGANIC VAPORS ON CLAY-MINERALS, Environmental science & technology, 27(10), 1993, pp. 2127-2132
The sorption of organic substances on Ca- and Na-kaolinite as well as
Ca-bentonite was studied at different temperatures and relative humidi
ties. The same general sorption behavior already encountered on quartz
sand in earlier experiments was also observed here. Sorption took pla
ce on a water film when the relative humidity exceeded the value which
was necessary to form a monomolecular layer of water on the adsorbenc
e. Above this relative humidity an inverse exponential relationship be
tween the sorption coefficient and relative humidity existed. At low h
umidities, when the coverage of the sorbent was incomplete, sorption w
as also possible at the unhydrated mineral surface, leading to a consi
derable increase of the sorption coefficients. Furthermore, the substa
nces could be divided into two groups on the basis of their heats of s
orption: the polar substances showed heats of sorption which were high
er than their corresponding heats of condensation due to their ability
to form hydrogen bonds, while for the unpolar compounds the opposite
was true. In addition to these general observations, the sorption beha
vior of single substances on the different sorbents was compared. The
differences in the sorption properties of kaolinite and quartz sand we
re apparently only due to the differences in their specific surface ar
eas. With bentonite, however, a somewhat different picture was encount
ered. While the heats of sorption were the same as observed for the ot
her sorbents, the slopes of the regression lines correlating In K and
relative humidity were about twice as high as those observed for kaoli
nite and quartz.