Molecular simulations of NAPL removal from mineral surfaces using microemulsions and surfactants

Abstract

Remediation of petroleum contaminants from aquifers is an ongoing and environmentally relevant challenge. Non-aqueous phase liquids (NAPLs) can infiltrate groundwater reservoirs and pollute the water source leading to health and public safety concerns. NAPLs such as asphaltenes and naphthenic acids possess high adsorptive potential making removal difficult with conventional pump-and-treat techniques. As a result, surfactants and microemulsions have been posited as a means of mobilizing and solubilizing these heavy contaminants for safe and effective removal. Experiments have shown that microemulsions with nonionic surfactants are effective for removing aquifer contaminants, although the exact molecular level mechanism is not clear. To this aim, molecular dynamics simulations were carried out with water, surfactant, and microemulsion solutions. These simulations were compared to determine the effects of surfactants and microemulsions on contaminant removal from calcite mineral surfaces. Results indicate that polar molecules serve as a base layer upon which further non-polar molecules could adsorb. Microemulsions were effective at swelling the oil phase and reducing the overall percentage of polar components, leading to easier removal. In addition, the dissociation of microemulsion micelles at the contaminant-water interface was shown to be a thermodynamically favorable process.