(465i) Adsorption and Remanence of Surfactants over Soil As Function of Mineralogy and Ionic Strength

Treating contaminated lands is a topic of interest due to the harms that these sites represent to the environment and to the nearby communities. In the United States, the Environmental Protection Agency (EPA) has reported more than 3000 contaminated sites according to the 2018 report[1]. In Mexico, the Federal Attorney for the Protection of the Environment (PROFEPA) has reported 1961 contaminated sites where 80% correspond to hydrocarbon spills[2].

When a spill occurs, most of the contaminants can remain free during a certain amount of time before migrating, and their concentration is still too high to think on a long-term treatment. One alternative when this occurs is soil flushing which generally is performed with water, and that can remove only the free contaminants. Some compounds such as poly-aromatic hydrocarbons (PAH) and heavy metals remain adsorbed to the minerals and hummus of soils. In this case, the cleaning is improved by injecting surfactant solutions. However, the first concern when injecting surfactants to the soil is that contaminants are first removed from the contaminated site, but they migrate to a different location such as water reservoirs. In addition, the surfactant may remain adsorbed to the surface of the soil, even if it is injected in very low concentration like when using foams.

Surfactant adsorption and remanence can affect the natural processes in the soil, and even worse when thinking on a natural recovery with autogenous microbiota. In this work, we evaluate the adsorption of an anionic, different non-ionic and bio-surfactant, over sand, calcium carbonate, and soil (collected from an agriculture site) as function of ions in the surfactant solution. In most of the cases we appreciate a monolayer adsorption at low ionic strength, and as the ionic strength concentration increases, the behavior turns to a multilayer adsorption behavior. The adsorption mechanism can be understood in terms of electrostatic interactions between the minerals in the soil and the chemical compounds and due to the lateral interactions between surfactant molecules[3]. This lateral interaction is also a function of ionic strength as reported by Nieto-Alvarez et.al. 2014[4], where the presence of salt induces the formation of vesicles instead of micelles. We also perform the study of remanence as a function of time and temperature. Ionic strength induces interactions that strongly affect the remanence of chemicals in the soil.

[1] U.S. Environmental Protection Agency 2017. Office of Land and Emergency Management (OLEM) Acomplishments Reports and Benefits. https://www.epa.gov/report-environment/contaminated-land

[2] https://semarnat.gob.mx/dgeia/informe 2018, “Residuos. 7.4.1. Sitios Contaminados”

[3] Paria, S.; Khilar, K.C. Adv. In Coll. And Interf. Sci., 2004, 110(3), 75-95

[4] Nieto-Alvarez, D.-A.; ET.AL. Langmuir, 2014, 30(41), 12243-12249