Abstract: A method for separating metals from metal-containing materials by extraction without generating large quantities of liquid waste is disclosed. Also disclosed is an extractant composition for use with this method. The method comprises exposing a metal-containing material to a solvent, such as supercritical carbon dioxide, an acid-base complex, and a chelating agent that is not a component of the acid-base complex. The metal is released into the solvent by a combination of oxidation by an oxidizing agent in the acid-base complex and chelation by the chelating agent. The oxidizing agent in the acid-base complex is solubilized by a solubilizing agent. The disclosed method and composition have many applications and are particularly well suited for the extraction of transition metals, including, but not limited to, platinum group metals, nom a metals and coinage metals. Applications include the recovery of metals from scrap materials and the planarization of semiconductor structures.