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- Recovery of platinum(IV) and palladium(II) from complex hydrochloric acid matrices by a thiodiglycolamide derivativePublication . Paiva, A. P.; Carvalho, G. I.; Costa, M. Clara; Costa, Ana M. Rosa da; Nogueira, CarlosThe solvent extraction performance of N,N’-dimethyl-N,N’-dicyclohexylthiodiglycolamide (DMDCHTDGA) towards Pt(IV) and Pd(II) in HCl solutions has recently been published. It was shown that these two platinum-group metals (PGMs) are efficiently extracted from 8 M HCl aqueous phases, being subsequently separated by sequential strippings: 1 M HCl allows Pt(IV) recovery, whereas Pd(II) is only back-extracted by thiourea in HCl. In this work, selectivity tests were carried out to evaluate the performance of DMDCHTDGA towards the recovery of both PGMs, from 8 M HCl aqueous phases, when in presence of Rh(III), Fe(III), Ni(II), Zn(II), Al(III), Ce(III) and Zr(IV), simulating the leaching solutions that may result from the hydrometallurgical treatment of spent automobile catalytic converters. It was generally observed that the additional metal ions do not affect the recovery of Pd(II) and Pt(IV) by DMDCHTDGA. Fe(III), Zn(II) and Zr(IV) are co-extracted with Pt(IV) and Pd(II); Fe(III) and Zn(II) were efficiently scrubbed with water, whereas Zr(IV) was removed by an acidified aqueous solution. Inversely, Ni(II) is not extracted, and Rh(III) and Ce(III) appear only traceably in the loaded organic phase. Al(III) is a concern, as it is appreciably extracted, and none of the tested backextraction solutions was able to strip it.
- Recovery of platinum and palladium from chloride solutions by a thiodiglycolamide derivativePublication . Paiva, A. P.; Carvalho, G. I.; Costa, M. Clara; Costa, Ana M. Rosa da; Nogueira, CarlosThe liquid-liquid extraction of platinum(IV) and palladium(II) from hydrochloric acid media was carried out using N,N’-dimethyl-N,N’-dicyclohexylthiodiglycolamide (DMDCHTDGA) in 1,2-dichloroethane (1,2-DCE). Pt(IV) is efficiently extracted from 5 M HCl onwards (%E = 97%), whereas Pd(II) is quantitatively recovered from 1 to 8 M HCl solutions. Both Pt(IV) and Pd(II) can be successfully stripped from the loaded organic phases, the former with a 1 M HCl solution, the latter with 0.1 M thiourea in 1 M HCl. The maximum loading capacity of DMDCHTDGA for Pt(IV) could not be determined but it is high, since molar ratios extractant:Pt(IV) within 2 and 3 have been achieved. Data obtained from successive extraction-stripping cycles suggest a good stability profile of DMDCHTDGA towards Pt(IV) recovery. Attempts to replace 1,2-DCE by more environmentally-friendly diluents showed, in general, comparable %E for Pt(IV). The study of the influence of acidity, as well as chloride ion and DMDCHTDGA concentrations, allows a proposal for the composition of the Pt(IV) species formed upon extraction. Results obtained with binary metal ion solutions point out that Pt(IV) and Pd(II) can be efficiently separated from DMDCHTDGA loaded organic phases through sequential selective stripping.
- N,N '-dimethyl-N,N '-dicyclohexylsuccinamide: a novel molecule for the separation and recovery of Pd(II) by liquid-liquid extractionPublication . Costa, M. Clara; Assunção, Ana; Almeida, Ruben; Costa, Ana M. Rosa da; Nogueira, Carlos; Paiva, A. P.ABSTRACT: N,N'-dimethyl-N,N'-dicyclohexylsuccinamide (DMDCHSA) is investigated as a potential molecule for the liquid-liquid extraction of Pd(II) from chloride solutions for the first time. The effect of several parameters on Pd(II) extraction, such as the contact period between both phases, hydrochloric acid, extractant and hydrogen ion concentrations, is evaluated. Pd(II) extraction equilibrium is very fast (30 s) and the extraction percentage (%E) increases with the HCI concentration in the aqueous phases, being higher than 60% for [HCl] > 5 M. The loading capacity of DMDCHSA for Pd(II) is reasonable (molar ratio extractant/metal higher than 16). Several stripping agents (e.g. distilled water, 1 M HCl, seawater and 20 g/L chloride solution as NaCl) were successfully used to transfer Pd(II) to a new aqueous phase, and data obtained from five successive extraction-stripping cycles suggest a good DMDCHSA stability pattern. Attempts to replace 1,2-dichloroethane (1,2-DCE) by commercial and more environmentally friendly diluents showed much worse %E for Pd(II). Selectivity tests with binary, ternary and more complex metal ion solutions were carried out to evaluate the performance of DMDCHSA towards Pd(II) recovery from 6 M HCl, when in presence of Pt(IV), Fe(III), Zn(II), Al(III) and Ce(III), metal ions usually present in solutions that may result from the hydrometallurgical treatment of spent automobile catalytic converters. It was generally observed that the additional metal ions do not affect the recovery of Pd(II) by DMDCHSA, although Fe(III) and Pt(IV) were co-extracted in a great extent. A solvent extraction (SX) scheme is proposed, based on a previous separation of Fe(III) with tributylphosphate (TBP) and on the selective and sequential stripping of Pt(IV) and Pd(II) from the loaded DMDCHSA with 0.01 M thiourea in 0.5 M HCI and seawater, respectively. The dependence of the Pd(II) distribution ratios on DMDCHSA and acidity, complemented with UV-Visible spectroscopy data, points out to DMDCHSA:Pd(II) extracted species with a 2:1 molar ratio and suggests the occurrence of an outer-sphere ion pair reaction, in which both [PdCl4](2-) and HCI are extracted.
- Leaching efficiency and kinetics of the recovery of palladium and rhodium from a spent auto-catalyst in HCl/CuCl2 mediaPublication . Nogueira, Carlos; Paiva, A. P.; Costa, M. Clara; Costa, Ana M. Rosa daABSTRACT: The recycling of scarce elements such as platinum-group metals is becoming crucial due to their growing importance in current and emerging applications. In this sense, the recovery of palladium and rhodium from a spent auto-catalyst by leaching in HCl/CuCl2 media was studied, aiming at assessing the kinetic performance as well as the influence of some processing factors, and the behaviour of contaminant metals. Based on a kinetic model developed for the present case, the influence of temperature was evaluated and the corresponding values of activation energy were estimated as 60.1 ± 4.1 kJ mol−1 for Pd and 44.3 ± 7.3 kJ mol−1 for Rh, indicating the relevance of the chemical step rather than diffusion. This finding was corroborated by the nonsignificant influence of the stirring velocity. The reaction orders were estimated for each leaching reagent: for HCl, values of 2.1 ± 0.1 for Pd and 1.0 ± 0.3 for Rh were obtained; for Cu2+, the obtained values were 0.42 ± 0.04 for Pd and 0.36 ± 0.06 for Rh. Without any significant loss of efficiency, solutions with higher metal concentrations were obtained using lower liquid/solid ratios, such as 5 L/kg. The main contaminant in solution was aluminum, and its leaching was found to be very dependent on the temperature and acid concentration.
- Recovery of palladium from a spent automobile catalyst leaching solution by a thiodiglycolamide derivativePublication . Paiva, A. P.; Carvalho, G. I.; Costa, M. Clara; Costa, A. M. R.; Nogueira, CarlosIn the sequence of previous research on the development of novel liquid-liquid amidetype compounds to efficiently and selectively extract platinum-group metals (PGMs) from concentrated hydrochloric acid media, a specific thiodiglycolamide derivative – N,N’-dimethyl-N,N’-dicyclohexylthiodiglycolamide (DMDCHTDGA) – has been applied for the recovery of palladium(II) from a spent automobile catalyst leaching solution, containing palladium(II) and rhodium(III) as PGMs. The results obtained are rather promising, since the DMDCHTDGA behavior towards the two PGMs is similar to that observed for hydrochloric acid aqueous media studied before, simulating the real leaching phases. Within eleven metal elements co-existing in solution, the majority in high fold-excesses, only aluminum(III) and cerium(III) interfere in the palladium(II) liquid-liquid extraction process, requiring further optimization.
- The solvent extraction performance of N,N’-dimethyl-N,N’-dibutylmalonamide towards platinum and palladium in chloride mediaPublication . Paiva, A. P.; Carvalho, G. I.; Costa, M. Clara; Costa, Ana M. Rosa da; Nogueira, CarlosThe 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 0.1Mthiourea in 1MHCl. 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.