Kinetic, complex formation and equilibrium studies of the adsorption of atrazine, diazinon and lindane on humic acids (HA) of various molecular weights (MW) were investigated. There was evidence that on HA with MW > 300,000 daltons, intraparticle diffusion of the adsorbate into the adsorbent particles was the rate limiting process. Complex formation of atrazine with HA was observed on HA with MW < 300,000 daltons with more atrazine being complexed at acid than at alkaline pH. This result was ascribed to the presence of more atrazine molecules in the protonated form. Ion exchange and hydrogen bonding reactions as well as electron transfer were in this case the mechanisms postulated.Equilibrium data of atrazine and lindane adsorbed on all HA fractions were explained by the Freundlich type isotherm whereas diazinon adsorption on HA with MW > 300,000 daltons followed the Langmuir type isotherm. Throughout the Investigation, adsorbate-adsorbent interaction was generally higher at pH 3.7 than at 7.0.

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This study was undertaken to evaluate sulfolane (tetrahydrothiophene-1, 1-dioxide) attenuation by soil and subsurface materials collected from a sour gas plant site using batch equilibration systems. The analyzed sample materials used in this study showed a wide range in terms of their selected physical and chemical properties. The reaction of sulfolane with the sample materials was fast initially and followed by slower rates at longer times. There was not much increase in the amount of sulfolane sorbed after about 5 hours of equilibration time irrespective of the temperature of the system. The rate of sorption of sulfolane followed a first-order reaction at both 25 and 8 degrees C temperature conditions and not affected by the temperatures range considered in this study. It appears that the sorption data of sulfolane on the various sorbents could be best described mathematically by the Freundlich equation. Kd values derived at 25 degrees C ranged from 0.05 to 0.88 L/kg and from 0.30 to 1.23 L/kg at 8 degrees C. Furthermore, increasing the ionic strength of the solution didn't affect sulfolane sorption by the various sorbents, which indicates that sulfolane sorption is not consistent with an ion-exchange mechanism but rather occurs through dipole-dipole interactions. Desorption of sulfolane was relative high in all systems. Multiple regression analysis shows a high level of correlation between Kd and several soil parameters. No sulfolane biodegradation was detected under anerobic conditions in any of the microcosms systems after 45 days of incubation at 25 and 8 degrees C, respectively. Sulfolane biodegradation data could be all fitted to zero-order kinetics. Biodegradation rates of sulfolane in the microcosms was the highest in sample depth 0-0.20 m, decreased with sample depth but significantly increased with the addition of nitrogen, and markedly decreased with temperature. At 25 degrees C and no supplement of N, biodegradation rate ranged from 4.26 to 12.70 mg/kg/day but with addition of N, the range was from 9.41 to 16.50 mg/kg/day.