Desorption hysteresis in five ion exchanged Montmorillonites

Jerry Paul Fairley, University of Nevada, Las Vegas


It is generally believed that the formation of recalcitrant (slowly desorbing) fractions of volatile organic compounds (VOCs) in soils is due to diffusion of compounds to sorption sites inaccessible to bulk fluid. The exact nature of these sites, however, is not well understood. In clay minerals, researchers favor two probable areas for the storage of persistent contamination; sites between the clay lamella, or sites within clay particle aggregates; To test the hypothesis that recalcitrant fractions are formed in interlamellar spaces, a Na/Ca Montmorillonite (Smectite) was ion exchanged with five different cations (K{dollar}\sp+,{dollar} Na{dollar}\sp+,{dollar} Ca{dollar}\sp{2+},{dollar} Mg{dollar}\sp{2+},{dollar} Fe{dollar}\sp{3+}){dollar} to form mineralogically similar clays with varying interlamellar environments. These soils were inoculated with an organic compound (toluene), incubated for 24 hours, and the recalcitrant fraction quantified for varying desorption times. The results did not show a clear correlation between persistent contamination and the interlamellar environment. Instead, evidence appears to support the conclusion that persistent contamination may be stored in clay particle microaggregates.