Solvent extraction of palladium(II) using diamides: A performing molecular system established through a detailed study of extraction kinetics

Abstract

Palladium isolation and refining through solvent extraction suffer from limited stability of commercial reagents or limited availability of robust reagents in nitrate media. Several performing extraction solvents based on diamide reagents have been proposed, but their preparation requires synthetic chemistry skills. In the present work, we propose the use of readily accessible N,N,N',N'-tetrahexylmalonamide (THMA). This reagent revealed superior distribution ratios and selectivity in comparison with previously used diamides for palladium(II) extraction from nitrate media in the frame of palladium recovery from waste. Furthermore, the benefit of excess dihexylamine (DHA) employed during the preparation of THMA was demonstrated through a gain in kinetics performance. Detailed analysis enabled to determine the best performing formulation of extraction solvent, which can be readily prepared from commercially available chemicals without any complex synthesis procedure nor purification step.

Extraction and Complexation Investigation of Palladium(II) by a Nitrilotriacetate-Derived Triamide Ligand

“…Therefore, a contact time of 30 min was adopted to ensure complete equilibrium in the subsequent extraction experiments. Although the extraction equilibrium time of NTAamide­( n -Oct) was slightly longer than that of malonamide ligand DMDBTDMA (<10 min), it was still faster than that of common N-donor ligands such as R-BTP (R = C2, C3, and C4) (>30 min) and C9-BTBP (>80 min).…”

“…Meanwhile, they belong to incompletely incinerable extractants and would also inevitably generate sulfur-bearing secondary waste, bringing troubles in nuclear waste management. , In contrast to S-donor ligands, amide and N-donor ligands have attracted wide attention because they not only have much better stability but also can be incinerated completely to gas products without any sulfur-bearing residual waste. Malonamide derivatives, such as N , N ′-dimethyl- N , N ′-dioctylhexylethoxymalonamide (DMDOHEMA), , N , N ′-dimethyl- N , N ′-dibutyltetradecylmalonamide (DMDBTDMA), − and N , N ′-dimethyl- N , N ′-dicyclohexyltetradecylmalonamide (DMDPHTDMA) , (Figure ), are the most representative amide ligands for the separation of Pd 2+ in HNO 3 and HCl solutions. However, this type of ligands has low extraction ability and poor selectivity for Pd 2+ .…”

Selective Recovery of Palladium (II) from Metallurgical Wastewater Using Thiadiazole-Based Chloromethyl Polystyrene-Modified Adsorbent

“…In recent decades, solvent extraction [ 10 ], chemical precipitation [ 11 ], membrane separation [ 12 ], ion exchange [ 13 ], and adsorption [ 14 , 15 ] have been widely applied to recover Pd from wastewater. Among these methods, adsorption offers the advantages of lower solvent consumption, no third-phase formation, and the ability to adsorb low-concentration solutions [ 16 ].…”