Metal extraction from heterogeneous surfaces using carbon dioxide microemulsions

We have demonstrated that water in carbon dioxide (w/c) microemulsions extr act copper and europium ions from a variety of solid substrates in high yie lds. The microemulsions are unique from bulk aqueous extractions in that th e volume of water used is similar to that of the metal extracted, rather th an that of the entire solid substrate, allowing grams of waste to be extrac ted with microliters of water. The microemulsion enhances wetting without s aturation of the solid matrix, allowing almost complete recovery of the met al ions. Our results show that > 98% of the metal can be recovered from a f ilter paper surface in a single extrtaction step. Extraction experiments us ing wood spiked with metal ions have shown that the microemulsions have enh anced diffusivity compared to bulk water. Pressure changes allow recovery a nd regeneration of the surfactant; in a test case, 81% of the initial capac ity is achieved upon reexposure of the w/c microemulsion to a second batch of copper nitrate.