Sorption and desorption by soils and sediments: Effects of sorbent heterogeneity

摘要

This dissertation describes an experimental pursuit of a mechanistic model for interpreting and quantitatively describing nonlinear, slow, and hysteretic sorption phenomena associated with heterogeneous soils and sediments in subsurface systems. The model is predicated on a hypothesis that soils and sediments comprise three predominant domains: an exposed mineral surface domain, a highly amorphous soil/sediment organic matter (SOM) domain, and a more condensed SOM domain; the latter domain is primarily responsible for the observed overall non-ideal sorption behavior.;Completely-mixed batch reactor systems were utilized to measure phenanthrene sorption and desorption for 9 inorganic model sorbents and 34 natural solids. The experimental program consisted of sorbent characterization, sorption and desorption equilibrium measurements, sorption rate determinations, and isosteric heat calculations. It has generally been shown from this extensive and broad investigation that sorption of phenanthrene by the exposed mineral Domain I and the amorphous SOM Domain II is near-linear, relatively fast, and completely reversible, and sorption by the condensed SOM Domain III is nonlinear, slow and only partially reversible. The distinctly different sorption behavior exhibited by these soil components is primarily determined by the physical and chemical characteristics of their associated surfaces and expandable matrices. Experimental investigations of isosteric heats of sorption revealed that the exposed, structurally rigid, and hydrophilic mineral Domain I favors interactions with water rather than phenanthrene. The soft SOM Domain II, being swollen by water and chemically compatible with phenanthrene, exhibits partitioning-like absorption. The hard SOM Domain III, on the other hand, demonstrates coupled nonlinear adsorption on external and intrinsic internal surfaces and slow absorption into expandable interiors of the matrices controlled by non-Fickian diffusion.