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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.
- New extractants for separation of platinium-group metals from chloride solutions and their application to recycling processesPublication . Paiva, A. P.; Carvalho, G. I.; Schneider, A. L.; Costa, M. Clara; Costa, A. M.; Assunção, A. F.; Nogueira, CarlosIn this paper some results on the application of four N,N’-tetrasubstituted malonamide derivatives for the extraction and separation of platinum-group metals (PGMs) are presented. The above mentioned extractants were specifically synthesized in order to evaluate their efficiency for the extraction of a specific metal, or group of metals, from aqueous chloride matrices. Different behaviours were obtained towards platinum(IV) and/or palladium(II) extraction, all the N,N’-tetrasubstituted malonamide derivatives allowing the mutual separation of the two metal ions, depending on the HCl concentration. Generally, extraction experiments were carried out involving initial aqueous phases containing 100 mg/L of each metal isolate, in varying 1M to 8M HCl concentration ranges, and 0.05M extractant in 1,2- dichloroethane solutions. From the preliminary results obtained, one can conclude that HCl concentrations and the structure of the malonamide derivative play a crucial role on the efficiency shown for Pt(IV) and/or Pd(II) extraction. The efficiency of the stripping stage of the loaded organic phases is variable, depending on the N,N’-tetrasubstituted malonamide derivative, as well as on the metal ion involved; for Pt(IV), distilled water and 1M HCl were generally successful, whereas for Pd(II), thiourea in HCl gave better results. The overall data already achieved suggest that these extractants may be good candidates for further evaluation in PGMs separations from real solutions resulting from recycling processes.
- Oxidative leaching process with cupric ion in hydrochloric acid mediafor recovery of Pd and Rh from spent catalytic convertersPublication . Nogueira, Carlos; Paiva, A. P.; Oliveira, Paula; Costa, M. Clara; Costa, Ana M. Rosa daThe recycling of platinum-group metals from wastes such as autocatalytic converters is getting growing attention due to the scarcity of these precious metals and the market pressure originated by increase of demand in current and emerging applications. Hydrometallurgical treatment of such wastes is an alternative way to the most usual pyrometallurgical processes based on smelter operations. This paper focuses on the development of a leaching process using cupric chloride as oxidising agent, in HCl media, for recovery of palladium and rhodium from a spent catalyst. The chloride media allows the adequate conditions for oxidising and solubilising the metals, as demonstrated by equilibrium calculations based on thermodynamic data. The experimental study of the leaching process revealed that Pd solubilisation is clearly easier than that of Rh. The factors temperature, time, and HCl and Cu2+ concentrations were significant regarding Pd and Rh leaching, the latter requiring higher factor values to achieve the same results. Leaching yields of 95% Pd and 86% Rh were achieved under optimised conditions (T = 80.C, t = 4 h,[HCl] = 6 M, [Cu2+] = 0.3 M).
- 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.
- Hydrometallurgical recovery of platinum-group metals from spent auto-catalysts: Focus on leaching and solvent extractionPublication . Paiva, A. P.; Piedras, Francisco Vega; Rodrigues, Pedro G.; Nogueira, CarlosABSTRACT: To ensure the supply of raw materials for products of extreme importance in strategic sectors, the recovery of critical metals from secondary sources becomes increasingly urgent. Platinum group metals (PGMs), being rare and very valuable, fall into this demand, and the catalytic converters that contain them are recognized as one of the main sources. Hydrometallurgical processes have been proposed as an alternative to pyrometallurgical ones, with leaching and separation by solvent extraction being core operations in this type of processing. This article investigates these two operations, seeking to optimize conditions and propose new arrangements to improve them. Two different catalyst samples were considered in the experimental work. Leaching was carried out involving concentrated HCl solutions (with H2O2 as oxidant) and low liquid/solid ratios, seeking to maximize PGMs recovery, guaranteeing their high concentration in leachates and minimizing aluminum co-dissolution. Cerium leaching was also followed since this is a rare-earth metal with potential interest. Temperature, HCl concentration, liquid/solid ratio (L/S), time and particle size factors were evaluated, and the optimized conditions found were 11.6 mol L-1 HCl, 1%vol H2O2, 60 C, L/S = 2 L kg(-1) and 3 h, leading to PGM yields of 90-98% Pt, 99% Pd and 70-96% Rh, and leachate compositions of 0.41-0.78 g L-1 Pt, 1.6 g L-1 Pd, 0.062-0.066 g L-1 Rh, depending on the catalyst sample.& nbsp;For solvent extraction (SX), several commercial extractants dissolved/diluted in toluene were checked, firstly with a model solution, and then applied to the real spent auto-catalyst (SAC) leachates produced in-situ. The overall results showed that the most promising SX systems among those tested were Cyanex (R) 471X and Cyphos (R) IL 101. Cyanex (R) 471X allowed the quantitative extraction of Pd(II) and Fe(III), but the latter was conveniently scrubbed by water prior to Pd(II) stripping by an acidic thiourea solution. Pt(IV) and Pd(II) extraction values by Cyphos (R) IL 101 were very encouraging, as only Fe(III) and Zn(II) were appreciably co-extracted, however, scrubbing of the contaminating metals, and Pd(II) and Pt(IV) stripping, did not work. Hence, investigation to find proper scrubbing/stripping agents for Cyphos (R) IL 101 SX system, to recover PGMs from recycled SACs, is further needed.
- Recovery of platinum from a spent automotive catalyst through chloride leaching and solvent extractionPublication . Méndez, Ana; Nogueira, Carlos; Paiva, A. P.ABSTRACT: Considering economics and environmental sustainability, recycling of critical metals from end-of-life devices should be a priority. In this work the hydrometallurgical treatment of a spent automotive catalytic converter (SACC) using HCl with CaCl2 as a leaching medium, and solvent extraction (SX) with a thiodiglycolamide derivative, is reported. The aim was to develop a leaching scheme allowing high Pt recoveries and minimizing Al dissolution, facilitating the application of SX. The replacement of part of HCl by CaCl2 in the leaching step is viable, without compromising Pt recovery (in the range 75-85%), as found for the mixture 2 M CaCl2 + 8 M HCl when compared to 11.6 M HCl. All leaching media showed good potential to recover Ce, particularly for higher reaction times and temperatures. Regarding SX, results achieved with a model solution were promising, but SX for Pt separation from the real SACC solution did not work as expected. For the adopted experimental conditions, the tested thiodiglycolamide derivative in toluene revealed a very good loading performance for both Pt and Fe, but Fe removal and Pt stripping from the organic phases after contact with the SACC solution were not successfully accomplished. Hence, the reutilization of the organic solvent needs improvement.
- 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.
- Ionic Liquids in the Extraction and Recycling of Critical Metals from Urban MinesPublication . Paiva, A. P.; Nogueira, CarlosABSTRACT: Ionic liquids (ILs), salts with a melting temperature below the boiling point of water, are one of the most recent fashion trends in modern chemistry. Nowadays, and taking into account the extensive research found in literature, it seems hard to imagine a sustainable world in the near future without the involvement of ILs, since they have low vapor pressure, are non-flammable, and display excellent chemical/electrochemical/thermal stabilities. Accordingly, ILs are considered to be advantageous replacers of the traditional organic solvents, therefore, much more environmentally-friendly. ILs can be easily produced to tune their physicochemical properties to specific applications, and that is the case currently occurring for several separation processes. This review aims to highlight and discuss some of the most relevant key-achievements, developed at laboratory scale, focusing on the use of ILs for the hydrometallurgical extraction of critical metals from urban mines, particularly the platinum-group metals (PGMs): ruthenium, rhodium, palladium, osmium, iridium, and platinum. A few decades of investigation brought a well-recognized scientific knowledge, still with a wide space to go, but work has yet to be conducted on testing the most promising ILs for the recycling of metals from real urban mines, and at a scaled-up level. Nevertheless, based on the most significant case-studies, the upcoming of ILs to recover critical metals from end-of-life devices for further valorization is assessed.