Identification of the Active Species for Scandium Extraction by Phoslex DT-8

Air-exposed di(2-ethylhexyl) dithiophosphate (Phoslex DT-8 (R)) has been previously shown to be ableto selectively extract scandium ions from waste water produced during zirconium refining. In the absence of exposure to air, Phoslex DT-8 (R) is not effective for scandium ion extraction, therefore, a compound produced by air-oxidation was suspected to be responsible for the selective extraction of the metal. In the present study, we employed P-31 NMR spectroscopy and mass spectrometry in order to identify this active species. We revealed that a sulfur atom of Phoslex DT-8 (R) was substituted for an oxygen atom on oxidation yielding O,O-bis(2-ethylhexyl) hydrogen thiophosphate (BOHTP). This compound was subsequently synthesized in high purity, and was confirmed to possess similar extraction capabilities for scandium as the oxidized Phoslex DT-8 (R).