(188aa) Design of a Foaming Formulation for Application in Remediation of Soils Contaminated with Hydrocarbons

Soil pollution by hydrocarbons has become a topic of national interest during the last years in Mexico. The reported environment emergencies due to chemical spills has increased in the period 20132 – 2017 from 627 to 1961 cases according to the Mexican Federal Attorney for Environmental Protection (PROFEPA) corresponding more than 85% to hydrocarbon spills [1,2]. During a hydrocarbon spill, residuals denominated as Dense Non-Aqueous Phase Liquids (DNAPL’s) remain adsorbed to the soil. These DNAPL are comprised mainly of heavy and polyaromatic hydrocarbons.

For removing these contaminants, processes as soil washing and waterflooding can be used, however, a chemical agent is in most cases required to remove the contaminants adsorbed to the soil grains by detergency. The use of traditional surfactants is not desired due to the risk of transporting the pollutants to other phase specifically to water bodies [3]. In this work, we present the alternative of using natural based foams to control the inundation of the surfactant during waterflooding. The expected benefits are the following: low amount of chemical injected in the foam, manageability due to the foam density and viscosity and biocompatibility due to the natural components of the formulation.

Different foaming formulations have been developed comprising: a natural surfactant, a natural viscosifier and a small amount of Sodium Dodecyl Sulfate (SDS) to improve foaming. The natural surfactant used is a saponin extracted from a cactus root and was provided by a fellow research group of the La Salle University Mexico. The natural viscosifier is cactus leave (opuntia ficus indica) mucilage, which was obtained by grinding cactus leaves with water and treating the mixture at 50°C for 24 hours, the supernatant is separated with the use of a centrifuge to separate suspended fiber and then dried in a “spray dryer” system, SDS was obtained by chemical product suppliers and used without further purification. Solutions were prepared using DI water or NaCl brines.

Foam stability tests were carried out for the different formulations by generating a foam column and measuring its volume as a function of time. Foam texture is also determined qualitatively by describing the size of the foam bubbles. The systems show faster initial drainage as the concentration of mucilage increases leaving stable dry foams. The stability of the dry foams increases notoriously with the presence of the mucilage using the same concentration of surfactants. We observe a limit of stability due to the concentration of SDS between 0.12% and 0.16% m/v; in this range the stability of the foams remains similar.

Mucilage seems to act also as ion trap. The presence of NaCl in the formulations does not affect the stability of the foams, thus the formulation can be used in saline environments.

To test the hydrocarbon ability of the formulations a simple test is carried out. Soil obtained from a random site is washed with water, and dried. The soil is then soaked with diesel and homogenized. Samples from the mixture are taken out and put in contact with water and the formulations. The solutions were mixed and then placed in the centrifuge. The recovered volume is then registered. Tests are carried by duplication. The presence of the formulations increases the removal of diesel in 16% in comparison to water.

In the same way, cactus leave mucilage is known to act as absorbant of oil in oil-water systems [4]. The formulations were put in contact directly with diesel and stirred. The formed emulsions were analyzed with the use of an optical microscope. Emulsions formed were O/W. Droplet size increases as the concentration of mucilage increases in the formulation. The presence of mucilage may give the oil-water interface more elasticity giving place to more stable and bigger oil droplets dispersed in water.

The work continues in our laboratory with the determination of rheology properties of the foams and analyzing their stability in terms of temperature. The foams are meant to be tested for compatibility in bioremediation processes and an injection system is being developed to continue with field tests in real contaminated soil.

[1] https://www.gob.mx/profepa/prensa January 2017, “Recibe PROFEPA 1,961 reportes de emergencias ambientales asociadas con sustancias químicas”

[2] http://semarnat.gob.mx/dgeia/informe 2014, “Residuos. 7.4.1. Sitios contaminados”

[3] Hernández-Soriano M.; Degryse, C.; Smolders, F. Environmental Pollution, 2011, 159(3), 809-816 "Mechanisms of enhanced mobilization of trace materials by anionic surfactants in soil"

[4] Alcantar, N.A.; Fox, D.I.; Thomas, S. US Patent Application Publication US 2013/0087507 A1 April 2013, “Use of cactus mucilage as a dispersant and absorbant for oil in oil-water mixtures”