Metal Extraction from Heterogeneous Surfaces Using Carbon Dioxide Microemulsions

Abstract

We have demonstrated that water in carbon dioxide (w/c) microemulsions extract copper and europium ions from a variety of solid substrates in high yields. The microemulsions are unique from bulk aqueous extractions in that the volume of water used is similar to that of the metal extracted, rather than that of the entire solid substrate, allowing grams of waste to be extracted with microliters of water. The microemulsion enhances wetting without saturation of the solid matrix, allowing almost complete recovery of the metal ions. Our results show that >98% of the metal can be recovered from a filter paper surface in a single extrtaction step. Extraction experiments using wood spiked with metal ions have shown that the microemulsions have enhanced diffusivity compared to bulk water. Pressure changes allow recovery and regeneration of the surfactant; in a test case, 81% of the initial capacity is achieved upon reexposure of the w/c microemulsion to a second batch of copper nitrate.