The Solvent Extraction Performance of N,N’-Dimethyl-N,N’-Dibutylmalonamide Towards Platinum and Palladium in Chloride Media

Abstract

The solvent extraction performance of N,N’-dimethyl-N,N’-dibutylmalonamide (DMDBMA) in 1,2-dichloroethane (1,2-DCE) towards platinum(IV) and palladium(II) in hydrochloric acid media was systematically evaluated. Pt(IV) extraction (%E) increases with the HCl concentration in the aqueous phases, being always higher than 72%, whereas Pd(II) extraction decreases from 65% at 1 M HCl to 22% at 8 M HCl. Several stripping agents for the two metals were tested: Pt(IV) is successfully recovered by a 1 M sodium thiosulfate solution, whereas the best result for Pd(II) was achieved with 0.1 M thiourea in 1 M HCl. The loading capacity of DMDBMA for Pt(IV) is high, and data obtained from successive extraction-stripping cycles suggest a good DMDBMA stability pattern. Attempts to replace 1,2-DCE by more environmentally-friendly diluents showed, in general, worse %E for Pt(IV). The dependence of Pt(IV) distribution coefficients on DMDBMA and chloride ion concentrations, as well as on acidity, are the basis of a proposal for the composition of Pt(IV) extracted species.

Keywords:

• platinum
• palladium
• N,N’-tetrasubstituted malonamide derivative
• solvent extraction
• hydrochloric acid

ACKNOWLEDGEMENTS

Thanks are also due to Exxon Mobil, Spain, and Shell Chemicals, Germany, for the diluent samples, to J. M. Nogueira and collaborators (CQB, DQB-FCUL) for GC-MS analysis, and to Sarah Bélair, from ERAMET, France, for the helpful discussions.

FUNDING

The financial support for the work reported in this article has been kindly provided by Portuguese national funds through “FCT - Fundação para a Ciência e a Tecnologia” (Lisbon, Portugal) under the project with the reference number PTDC/QUI-QUI/109970/2009, including the investigation grant offered to G. I. Carvalho.