Metal extraction using tri-n-butyl phosphate

Full text: The Moessbauer group at Monash University has been working for several years on the extraction of gold onto polyurethane foams as an alternative to the conventional activated carbon. An advantage of polyurethane foams is that they can be loaded with suitable extractants such as tri-n-butyl phosphate (TBP) during their manufacture. TBP is used as an extractor for gold and other metals including the rare earths. In our experiments TBP has extracted metals from aqueous metal / salt solutions which is the mechanism under investigation. Moessbauer spectra at liquid nitrogen temperature on rapidly frozen solutions of TBP in the carrier xylene have been taken from iron-loaded and europium-loaded acidic solutions. The results show that iron is extracted from solution as Fe(III) in low and high acid concentrations and maybe as Fe(II) in low acid concentrations. The spectra indicate that iron is in the high spin state and may be tetrahedrally or octahedrally coordinated. Possible species include H2(TBP)2.Fe(III)(SO4)4, H(TBP)2.Fe(III)Cl4, and Fe(III)Cl3.3TBP with an arrangement of water molecules. Europium has been found to be extracted as Eu(III) only. Further experiments with gold and gadolinium are planned to investigate the bonding process of TBP