Retrieval and reuse of surfactants from microemulsions enabled by a pH‐triggered precipitation‐dissolution strategy

How to retrieve and reuse surfactants efficiently from surfactant‐based microemulsions (MEs) has long been a problem, which is full of challenges and needs to be solved urgently. To this end, a pH‐triggered precipitation‐dissolution (PTPD) strategy is developed. The surfactant sodium 3‐(laurylamino)propane‐1‐sulfonate (LMPS) transforms into an insoluble precipitate (the inner salt of LMPS, LMP) after reaction with HCl, by which the monophasic LMPS‐based MEs demulsified entirely, giving a separable mixture of oil, water and LMP. LMP can be retrieved efficiently (~95.3 %) regardless of the ME type, and can then be conveniently restored to LMPS via reactions with NaOH. Conceptually, the retrieval of LMPS (~96.6 %), toxic benzo[a]pyrene (BaP, ~99.5 %) and a mixture of co‐surfactant n ‐butanol and the oil phase n ‐heptane (~97.1 %) from the sufficiently emulsified soil eluents is achievable by respectively using the PTPD strategy and distillation, wherein the soil eluents were generated from the remediation of BaP‐contaminated soil using an oil‐in‐water LMPS‐based ME as washing agent. It reveals a promising future for the PTPD strategy in the post‐processing of soil eluents containing toxic hydrophobic organic contaminants and excessive surfactants.