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Sorption of Para-Xylene Vapors on Salt-Treated Soils Measured by Flow-Equilibration and Gas Chromatography Methods

Soil and Water Science Dep., 2171 McCarty Hall, Univ. of Florida, IFAS, Gainesville, FL 32611-0151;
Dep. of Civil and Environ. Eng., 1351 Beal Ave., 181 Eng. Bldg. 1A, The Univ. of Michigan, Ann Arbor, MI 48109-2125.

^* Corresponding author.

ABSTRACT

The impact of soil properties other than organic C content and surface area on vapor-phase sorption has rarely been considered. This study was conducted to determine the effect of salt, namely CaCl₂, on the sorption of p-xylene vapor under anhydrous and hydrated conditions. Sorption on Webster soil (Typic Haploquolls) before and after removal of organic C was measured using a flow-equilibration method. In addition, the utility of an eluted pulse gas chromatography method was evaluated using the sand fraction of Oldsmar soil (Alfic Arenic Haplaquods) as a column-packing material. The CaCl₂ significantly decreased p-xylene sorption at both 0 and 90% RH for both adsorbents. Under anhydrous conditions, reduced sorption by Oldsmar sand was evidenced at low p-xylene vapor pressures by a constant net retention volume and symmetrical peaks, indicating linear sorption and ideal behavior at these vapor pressures (i.e., the Henry's region). In the absence of salt, the net retention volume continued to increase at p-xylene vapor pressures as low as 0.33 Pa, indicating isotherm nonlinearity, even at this low vapor pressure. This difference in retention behavior suggests that salt modified the nature of the surface of the sorbents. Under hydrated conditions, the reduction in sorption may be related to the salting-out effect of CaCl₂ on gas solubility in adsorbed water films. These data suggest that the distribution and migration of organic vapors may be substantially greater in salt-affected soils due to reduced sorption on both the dry and water-coated solid phases that are present.

Florida Agric. Exp. Stn. Journal Series no. R-02860.

Received for publication August 17, 1992.