A Distributed Reactivity Model for Sorption by Soils and Sediments. 6. Mechanistic Implications of Desorption under Supercritical Fluid Conditions

Abstract

Phenanthrene desorption isotherms for five dry soil materials were measured in supercritical carbon dioxide (SC CO 2 ) at up to 12 different temperature (40-60 °C) and pressure (120-310 atm) conditions for each soil. The Freundlich model adequately described all 40 isotherms obtained. At each condition, sorption capacity increased with increasing organic matter content with a positive dependence on oxygen content. Trends in desorption with SC CO 2 temperature and pressure were qualitatively consistent with variations in phenanthrene solubility. A diagenetically altered shale material displayed desorption increases similar in magnitude to solubility changes, but increased pressure stimulated desorption from surface soils far less than expected from solubility considerations. Swelling of amorphous macromolecular soil organic matter (SOM) in the non-shale materials at higher SC CO 2 pressures is postulated to increase the sorption capacity of the SOM phase, largely offsetting the increased capacity of the solvent phase that accompanies pressure increases. The results extend application of the distributed reactivity model (DRM) to nonaqueous solvents and dry soil systems and lend additional support to the mechanistic importance of rigid or glassy SOM domains in the sorption of non-ionic organic chemicals.

Sorption of phenanthrene and benzene on differently structural kerogen: Important role of micropore-filling

“…The dual-sorption model has characterized NOM as two domains containing absorption (partitioning) and adsorption (micropore-filling) phases (Weber and Huang, 1996;Weber and Young, 1997;Xing and Pignatello, 1997;Ran et al, 2003). Kerogen is a form of NOM that has undergone geochemical diagenesis.…”

The PT/S-Box of Modular Cellulase AcCel12B Plays a Key Role in the Hydrolysis of Insoluble Cellulose

“…The amount of desorbed protein was determined from the UV absorption values at 280 nm ( Figure 5) and analyzed by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) ( Figures S3 and S4). The Freundlich (equilibrium) model is a commonly used approach for determining reagent distribution between solid and solution for both adsorption and desorption processes [41,42]. We used the Freundlich model to determine cellulase desorption.…”

“…All figures were described as AcCel12B-PT0 (dashed dotted line and ◊), AcCel12B-PT1 (dotted line and ▲), AcCel12B-wt (dashed line and ○), and AcCel12B-PT3 (solid line and ■). Furthermore, n in Table 5 indicates sorption intensity [44], or the energy of desorption [42]. The n values of wild-type and mutant AcCel12B desorbing from Avicel reduced gradually with the number PT/S-box units in a step of approximately 0.4 per PT/S-box unit added.…”

JV Task 92 - Alcoa/Retec SFE and SPME

“…Supercritical fluid extraction (SFE) with pure carbon dioxide (CO2) has recently been proposed as a potentially rapid method to determine the "availability" of soil-and sediment-bound organics (43)(44)(45)(46)(47). The potential advantage of SFE is that the solubility of target analytes can be varied continuously over several orders of magnitude by controlling the extraction pressure and temperature (48,49).…”

“…However, in a recent series of articles, SFE performed under increasingly stronger conditions showed that PCBs were present in several different types of sites on every soil and sediment tested and that PCBs were associated with sites ranging from "fast" (extracted at the mildest SFE conditions) to "slowly desorbing" sites (45)(46)(47). Furthermore, when the same sediments were exposed to PCBs in water for up to 18 days, the exposure time was only sufficient for the PCBs to sorb to only the "fast" sites, demonstrating that very long exposure times would be needed for the PCBs to gain the "slowly desorbing" sites which were occupied in the original environmentally aged sediments (47).…”