Browsing by Author "Carvalho, G. I."
Now showing 1 - 6 of 6
Results Per Page
Sort Options
- 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.
- 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.
- 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.
- 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 precious metals from exhausted automotive catalysts by leaching and solvent extractionPublication . Nogueira, Carlos; Carvalho, G. I.; Costa, M. Clara; Costa, Ana M. Rosa da; Paiva, A. P.Platinum group metals (PGM’s) are precious and rare metals used in many existing and emerging technologies such as electronics, catalysts, energy and medical appliances, among others. PGM’s applications and demand are growing rapidly, and their supply is short and considered critical. Recycling of residues containing PGM’s is therefore mandatory, in order to allow the continuity of supplying. The main market share of PGM´s are catalysts, specially automotive catalytic converters. When exhausted, these wastes constitute important secondary resources that cannot be neglected. Therefore, the recycling of autocatalysts has been taken growing attention. Although some refiners operating plants for PGM’s recovery from residues are already known, the processes are complex, involve many operations and are highly reagent-consuming. Research in this domain is increasing, trying to develop new technologies and processes, more efficient and selective, and less consuming. Hydrometallurgy, and specifically solvent extraction with new reagents, can play an important role in achieving those objectives. In this context, a research has been carried out aiming at developing hydrometallurgical technologies to recover PGM's from spent autocatalysts. This paper presents some results of this investigation, namely concerning the leaching and solvent extraction operations. A Pd-Rh bearing catalyst was mechanically treated by shredding with a cutting mill, allowing size reduction to average particle size of d50=0.61 mm. The leaching operation was tested using hydrochloric acid media (6 M) and several concentrations of nitric acid as oxidizer (0.5-2.4 M). The results attained showed that the dissolution of Pd and Rh was very efficient, with yields near 90%, whatever the nitric acid concentration used. The extraction and separation of PGM’s from synthetic aqueous solutions was studied with amide extractants, namely an N,N’-tetraalkyl substituted thiodiglycolamide. The results showed a good selectively of this extractant for palladium against rhodium, allowing 100% Pd extraction in a wide range of HCl concentrations (1-8 M), while Rh extraction was near 65%. The complete selectivity can be however attained in the subsequent stripping operations, given that Pd can be quantitatively stripped with thiourea/HCl solutions while Rh co-extracted is only stripped by a soda solution. Platinum, if present in the catalysts, can also be processed by this extractive system, since it is also extracted mainly for high HCl concentrations in leachates, and can be selectively stripped by diluted HCl solutions. The achieved results seem promising for developing a new process for efficient separation and recovery of PGM’s from catalysts, using acid leaching and highly selective solvent extraction technology.
- 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.