Dissolution Kinetics of n-Alkanes From TPH Contaminated Soils: The Effect of Ionic Strength.

             Dissolution of n-alkanes from TPH (Total Petroleum Hydrocarbon) contaminated soil has not been well studied.  The objective of this study was to investigate the effect of ionic strength on the dissolution of n-alkanes from the soil particles to the aqueous phase.  TPH contaminated soils were sampled from the site used for former oil storage tank for over 50 years, in Gyeonggi, Korea.  The dissolution concentration of each n-alkane was obtained as a function of electrolyte concentrations (0, 1, 5, 20mM, and 1M CaCl₂); the experiment was performed for 3hr ~ 16d at room temperature (25±2^oC).  The chemical analysis was carried out with GC/FID-17A (Shimadzu, Japan), using TRPH Standard as the external standard.  The concentration of n-alkanes with even carbon number between C10 ~ C20 was measured.  The dissolution kinetics of lower molecular weight n-alkanes (C10 and C12) were found to follow the first order kinetics at the lower ionic strength (0, 1 and 5mM).  However, the dissolution kinetics of lower molecular weight n-alkanes was not well fitted with the first order kinetics at the higher ionic strength (20mM and 1M).  When the ionic strength concentration was lower, the time required to reach equilibration was shorter.  The equilibration dissolved concentration of even n-alkanes was highest in 1mM CaCl₂ solution.  In the higher ionic strength solution (20mM and 1M), the dissolved n-alkanes were assumed to resorb to the soil particle after 12 ~ 24hr.  The salts in electrolytes were found to induce more dissolution of the n-alkanes than the distilled water.  However, in higher salt concentration (e.g., 20mM and 1M) the dissolved concentration of n-alkanes was decreased due to salting-out effect.  The equilibrium concentration was reduced by the salting-out effect, as the solution concentration was higher.