Scientists in Canada have shown they can recover oil from contaminated sand using surfactants whose emulsion stabilising ability is deactivated by carbon dioxide.
Land-based oil spills can be remedied by taking the sand (or soil away) for washing. The sand is heated and mixed with a surfactant solution, before the oil containing emulsion is removed to leave clean sand. However, the entire emulsion must be disposed of as hazardous waste.
Switchable surfactants could offer a less wasteful solution. Unlike normal surfactants, switchable surfactants can be switched off by an external trigger, allowing the oil and water phases to separate, by destabilising the emulsion.
The negative surface charges on sand particles mean that surfactants for cleaning oil contaminated sand need to be anionic. Cationic switchable surfactants were pioneered by Philip Jessop and his colleagues at Queens University, Kingston, Ontario, in 2006, and now the team have created an anionic version.
To release oil captured by Jessop’s carboxylate and phenolate anionic surfactants carbon dioxide is bubbled through the emulsion, acidifying the aqueous phase. This switches the surfactant structure from anionic to neutral, disrupting the emulsion by removing its ability to stabilise the oil/water interface. The oil separates and can be decanted for reuse and sale. Decarbonising the solution will switch the surfactants back on.
Read the rest of the story by Emily Skinner in Chemistry World!
Read the original research paper in RSC Advances:
Switchable anionic surfactants for the remediation of oil-contaminated sand by soil washing
Elize Ceschia, Jitendra R. Harjani, Chen Liang, Zahra Ghoshouni, Tamer Andrea, R. Stephen Brown and Philip G. Jessop
RSC Adv., 2014, 4, 4638-4645
DOI: 10.1039/C3RA47158F, Paper