Optimum concentration of fly ash nanoparticles to stabilize CO2 foams for aquifer and soil remediation.

Abstract

Contamination caused by non-aqueous phase liquids (NAPLs) in aquifers and soil is an important challenge that requires effective remediation techniques. One potential approach is through the use of CO2 foams to displace NAPLs from permeable media. CO2 foams generated only by surfactants are not stable enough for the efficient removal of NAPLs contamination. This shortcoming may be alleviated via the use of nanoparticles (NPs)-surfactant mixtures as a stabilizing agent. This work focuses on the evaluation of the optimum concentration of fly ash nanoparticles for stabilizing CO2 foam with the combined action of the surfactant. The performance of this foam is evaluated in remediating a contaminated 41\xa0mm\xa0×\xa036\xa0mm surrogate permeable medium in a microfluidic device. Mixtures of fly ash, a by-product of coal-burning power plants, and alpha-olefin sulfonate (AOS) and lauramidopropyl betaine (LAPB) surfactants are used to generate stable foams. The results show that a 1000\xa0mg/L AOS-LAPB surfactant solution along with 1000\xa0mg/L of fly ash NPs produces the best performance. Formation of deposits in the matrix is observed. These deposits, which are more prominent at higher NP concentrations, appear to adversely affect displacement, displacement efficiency and remediation of the medium. This study demonstrates that using fly ash nanoparticles and optimizing their concentration can effectively stabilize CO2 foams and improve the displacement efficiency for aquifer and soil remediation.