EFFECTS OF TEMPERATURE AND RELATIVE-HUMIDITY ON THE SORPTION OF ORGANIC VAPORS ON CLAY-MINERALS

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.