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- N,N′-tetrasubstituted succinamides as new molecules for liquid–liquid extraction of Pt(IV) from chloride mediaPublication . Costa, Maria Clara; Almeida, Ruben; Assunção, Ana; Costa, Ana M. Rosa da; Nogueira, Carlos; Paiva, Ana PaulaDue to the increasing demand of platinum group metals (PGM’s), among which platinum, the search for new alternatives aiming to their extraction and recovery is nowadays of great importance. Thus, two N, N0-tetrasubstituted succinamides, N,N0-dicyclohexyl-N,N0-dimethylsuccinamide (DMDCHSA) and N,N0- dimethyl-N,N0-diphenylsuccinamide (DMDPHSA) were synthesized and investigated, for the first time, as potential molecules for the liquid–liquid extraction of Pt(IV) from chloride solutions. According to the extraction and stripping results obtained in a single contact, these succinamides can be considered promising extractants for the recovery of platinum(IV) from hydrochloric acid media, since DMDCHSA is able to extract more than 95% Pt(IV) from 4 M HCl or higher concentrations, and DMDPHSA extracts 80% and 92% Pt(IV) from 6 M and 8 M HCl solutions, respectively. Furthermore, platinum(IV) can successfully be stripped through a simple contact with seawater: 93% Pt(IV) were recovered from DMDCHSA, while 60% stripping were obtained from DMDPHSA. For each compound, the time necessary to reach equilibrium, and the effects of the type of diluent and different extractant concentrations on the Pt(IV) extraction percentage were investigated. The loading capacity of DMDCHSA and DMDPHSA toward Pt (IV) was also evaluated, and the results show that both extractants present a very high loading capacity. In addition, data obtained from successive extraction-stripping cycles suggest a good stability pattern for both succinamides.
- A bridge between liquid-liquid extraction and the use of bacterial communities for palladium and platinum recovery as nanosized metal sulphidesPublication . Assunção, Ana; Matos, Ana; Costa, Ana M. Rosa da; Candeias, Antonio; Costa, Maria ClaraThe Platinum Group Metals (PGM) are rare in the Earth's crust and in the past years their use had a considerable expansion limiting their availability, which justifies PGM's high commercial value and demand. Therefore, PGM recovery from secondary sources is very important from both economic and environmental points of view. In recent years, several methods for PGM removal have been investigated. Our research group has been studying the removal/recovery of PGM using both chemical (liquid liquid extraction) and biological methods (using anaerobic bacterial communities).The aim of this study was to combine these two chemical and biological approach technologies, for PGM recovery. For that purpose, Pd(II) and Pt(IV) present in aqueous phases, were extracted to organic phases composed by N,N'-dimethyl-N,N'-dicyclohexylsuccinamide (DMDCHSA) and N,N'-dimethyl-N,N'-dicyclohexyltetradecylmalonamide (DMDCHTDMA) in 1,2-dichloroethane, respectively, with an extraction efficiency of 79% for Pd(II) and 99% for Pt(IV). The metals in the loaded organic phases were then stripped with seawater, a low-cost solution largely available in nature, with efficiencies of 100% for Pd and 86% for Pt. Finally, the metals were precipitated and recovered using metabolic products produced by a community enriched for sulphate-reducing bacteria. The palladium precipitated completely, while 86% of platinum was precipitated. During the precipitation process sulphide concentration in the solution decreased and the analysis of the precipitates was consistent with the formation of nanosized PdS and PtS2.To our knowledge, this research shows, for the first time, the potential of combining liquid liquid extraction with the use of bacteria aiming platinum and palladium recovery, as metal sulphides, from aqueous media. (C) 2016 Elsevier B.V. All rights reserved.
- Liquid-Liquid Extraction of Platinum from Chloride Media byN,N′-Dimethyl-N,N′-DicyclohexyltetradecylmalonamidePublication . Costa, Maria Clara; Assunção, Ana; Costa, Ana M. Rosa da; Nogueira, Carlos; Paiva, Ana PaulaLiquid-liquid extraction of platinum(IV) from chloride media was carried out using N,N - dimethyl-N,N -dicyclohexyltetradecylmalonamide (DMDCHTDMA) in 1,2-dichloroethane. Platinum can be effectively extracted by DMDCHTDMA without addition of tin(II) chloride, since extraction percentages (%E) of 88% and 99% have been achieved from 6 M and 8 M HCl, respectively. Moreover, platinum can be successfully stripped through a simple contact with a 1 M HCl solution. The effect of some experimental parameters such as equilibration time, diluent, extractant and HCl concentrations was systematically investigated. The loading capacity of DMDCHTDMA was also evaluated. Data obtained from successive extraction-stripping cycles suggest a good stability pattern of DMDCHTDMA. Preliminary extraction data achieved with single metal ion solutions pointed out to a possible separation of platinum(IV) from palladium(II).