Palladium Isolation and Purification from Nitrate Media: Efficient Process Based on Malonamides

ABSTRACT

Solvents based on malonamides have been described to be very efficient and selective for liquid-liquid extraction of Pd(II) from nitrate media. The present study details the possibility to selectively extract Pd(II) over common metallic cations, Cu(II), Ni(II), Co(II), Zn(II), Nd(III), Fe(III) and Al(III) using N,N’-dimethyl,N,N’-dibutyltetradecylmalonamide (DMDBTDMA) in toluene. The lowest selectivity was obtained considering Fe(III) and Nd(III), the extraction of all other cations being negligible. Pd(II) distribution and selectivity regarding Fe(III) have been fine-tuned using the aqueous HNO₃ concentration as the sole parameter, so that extraction, scrubbing and stripping steps can be simply designed without the need for other specific metal chelating reagents and/or aqueous media and without the extensive generation of aqueous effluents. DMDBTDMA was also benchmarked with other classical Pd(II) extractants such as tributylphosphate (TBP), dihexylsulfide (DHS), tetraoctyl diglycolamide (TODGA) and bis(2-ethylhexyl)sulfoxide (BESO) in toluene and in n-heptane. Overall, this study reveals that malonamides are very well positioned and should be considered for further processing of aqueous nitrate wastes containing Pd contaminated with common base metals.