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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).
- Application of urea-agarose gel electrophoresis to select non-redundant 16S rRNAs for taxonomic studies: palladium(II) removal bacteriaPublication . Assunção, Ana; Costa, Maria Clara; Carlier, JorgeThe 16S ribosomal RNA (rRNA) gene has been the most commonly used sequence to characterize bacterial communities. The classical approach to obtain gene sequences to study bacterial diversity implies cloning amplicons, selecting clones, and Sanger sequencing cloned fragments. A more recent approach is direct sequencing of millions of genes using massive parallel technologies, allowing a large-scale biodiversity analysis of many samples simultaneously. However, currently, this technique is still expensive when applied to few samples; therefore, the classical approach is still used. Recently, we found a community able to remove 50 mg/L Pd(II). In this work, aiming to identify the bacteria potentially involved in Pd(II) removal, the separation of urea/heat-denatured DNA fragments by urea-agarose gel electrophoresis was applied for the first time to select 16S rRNA-cloned amplicons for taxonomic studies. The major raise in the percentage of bacteria belonging to genus Clostridium sensu stricto from undetected to 21 and 41 %, respectively, for cultures without, with 5 and 50 mg/L Pd(II) accompanying Pd(II) removal point to this taxa as a potential key agent for the bio-recovery of this metal. Despite sulfate-reducing bacteria were not detected, the hypothesis of Pd(II) removal by activity of these bacteria cannot be ruled out because a slight decrease of sulfate concentration of the medium was verified and the formation of PbS precipitates seems to occur. This work also contributes with knowledge about suitable partial 16S rRNA gene regions for taxonomic studies and shows that unidirectional sequencing is enough when Sanger sequencing cloned 16S rRNA genes for taxonomic studies to genus level.
- Ensaios para redução de bromato por adsorção com carvão activado em póPublication . Assunção, Ana; Lucas, Helena; Sancho, Rui; Barros, Raúl José Jorge deNos dias que decorrem o conceito “água potável” tem-se revelado da maior importância para a humanidade, pelo que a exigência da sua qualidade e distribuição, por todo o planeta, tem sido cada vez maior. No processo de tratamento da água para consumo humano uma etapa importante (oxida matéria orgânica, metais, algas e bactérias) e crítica (forma sub-produtos indesejáveis) é a pré-oxidação. No caso de se utilizar como agente oxidante o ozono e da água a tratar conter o ião brometo de origem natural, forma-se, o bromato, que tem sido considerado potencialmente cancerígeno para o ser humano, pelo que, o valor paramétrico (VP) actualmente imposto por lei, de 25μg/L, será alterado a partir de 25 de Dezembro de 2008, para o VP de 10μg/L, de forma a garantir maior segurança da saúde pública. Este trabalho, realizado na Águas do Algarve, S.A., nomeadamente na Estação de Tratamento de Água (ETA) de Alcantarilha, que tem como água bruta a tratar a mistura de duas origens de água, superficial e subterrânea e, teve o objectivo de ensaiar laboratorialmente diferentes condições operacionais com diferentes tipos de carvão activado em pó (CAP) e identificar, se possível, aquele que obtém melhores resultados na remoção de bromato, para posterior aplicação à escala real, nos processos de tratamento de água para consumo humano. Os ensaios realizaram-se em “jar-test”, simulando as condições existentes na ETA, para o caudal máximo e mínimo numa linha de tratamento, testando-se 3 tipos de CAP e um branco (sem CAP), para 3 concentrações de bromato. Os resultados revelaram que era possível com qualquer um dos 3 carvões estudados remover o ião bromato, mas apenas para concentrações iguais ou superiores a 60μg/L, concluindo-se que o uso destes carvões não seria a melhor opção para remover/reduzir quantidades relativamente baixas (≤15μg/L), como acontece no caso estudado. Perante tais resultados sugere-se que sejam testadas duas possibilidades para remover/reduzir o ião bromato da água tratada na ETA de Alcantarilha, nomeadamente a separação das origens de água, seguindo processos de tratamento distintos ou a realização de ensaios com carvão activado granular (CAG) ou com filtros de biológicos de carvão activado (BAC) para averiguar a possibilidade da sua aplicação na ETA de Alcantarilha
- Recovery of gold(0) nanoparticles from aqueous solutions using effluents from a bioremediation processPublication . Assunção, Ana; Vieira, Bernardete; Lourenço, J. P.; Costa, Maria ClaraThe use of biological processes with the aim of the recovery of gold from low-concentration solutions derived from leaching of secondary sources is gaining increasing importance owing to the scarcity of the primary resources and the economic and environmental advantages usually presented by these methods. Thus, the addition in batch and continuous processes of different solutions containing biogenic sulphide, which was generated by the activity of sulphate-reducing bacteria (SRB), to gold(III) solutions was investigated for that purpose. In the batch experiments, AuS nanoparticles with sizes of between 6 and 14 nm were obtained (corresponding to 100% removal of Au(III) from solution) if the biogenic sulphide was generated in a typical nutrient medium for SRB, whereas Au(0) nanoparticles with sizes of below 8 nm were obtained (corresponding to 62% removal of Au(III)) if effluent from a SRB bioremediation process for treating acid mine drainage (AMD) was used instead. These results stimulated the development of a continuous process of addition, in which two sulphide-rich effluents, which resulted from a SRB bioremediation process for treating two types of AMD (from a uranium mine and a polysulphide mine), were tested. In both cases, Au(0) nanoparticles with sizes of between 6 and 15 nm were mainly obtained, and the percentage removal of Au(III) from solution ranged from 76% to 100%. The processes described allow the simultaneous treatment of AMD and recovery of metallic gold nanoparticles, which are a product with a wide range of applications (e.g., in medicine, optical devices and catalysis) and high economic value. The synthesis process described in this work can be considered as novel, because it is the first time, to our knowledge, that the use of effluent from a SRB bioremediation process has been reported for the recovery of gold(III) as gold(0) nanoparticles.
- Biological and chemical strategies for the recovery of precious and rare metals as nanoparticlesPublication . Assunção, Ana; Costa, Maria ClaraThe present work explored the potential of chemical (solvent extraction) and biological (using anaerobic bacterial community) technologies, aiming the removal/recovery of precious metals from aqueous solutions. Solvent extraction or liquid-liquid extraction was used to find a suitable platinum and palladium extractant, to be applied to the treatment of aqueous solutions containing these metals. Thus, N,N’-dimethyl-N,N’-dicyclohexyltetradecylmalonamide (DMDCHTDMA), N,N’-dicyclohexyl-N,N’-dimethylsuccinamide (DMDCHSA) and N,N’-dimethyl-N,N’-diphenylsuccinamide (DMDPHSA) were tested and proved to be efficient at extracting platinum (IV) from HCl solutions. Platinum (IV) was then successfully stripped from DMDCHTDMA using 1 M HCl solution, and from DMDCHSA and DMDPHSA, using seawater. These extractants proved to be less efficient for palladium (II) removal, thus, for this metal, biological strategies were tested. A palladium (II)-resistant bacterial community, able to biorecover palladium from solutions, was found. The phylogenetic analysis showed that this community was mainly composed by bacteria close to Clostridium species, however, bacteria affiliated to genera Bacteroides and Citrobacter were also identified. The potentialities of combining solvent extraction and the use of bacterial communities for palladium and platinum recovery were also demonstrated. Pd(II) and Pt(IV) in aqueous phases were efficiently extracted to organic phases. The metals were then stripped with seawater, precipitated and recovered using a filtered solution from bacterial growth. The successful precipitation of palladium (II) and platinum (IV), as nanosized PdS and PtS2 particles, was accompanied by sulphide concentration decrease in the bacterial growth solution. Biological processes, using effluents from an acid mine drainage bioremediation treatment system, were tested for gold recovery from aqueous solutions. The use of these effluents, with dissolved biogenic sulphide, proved to be an excellent alternative for Au(III) recovery as Au(0) nanoparticles (NPs). Finally, biogenic sulphide, from the effluents tested before, was also used to successfully synthesize Ag2S NPs and Ag2S/TiO2 nanocomposite. The Ag2S NPs and Ag2S/TiO2 nanocomposite obtained have semiconductor properties and can theoretically be used for radiation based applications.
- Performance and bacterial community shifts during phosphogypsum biotransformationPublication . Martins, Mónica; Assunção, Ana; Neto, André; Silva, Gonçalo; Sghaier, Haitham; Costa, Maria ClaraPhosphogypsum (PG) is an industrial waste composed mainly by sulfate, turning it a suitable sulfate source for sulfate-reducing bacteria (SRB). In the present work, the capability of two SRB communities, one enriched from Portuguese PG (culture PG) and the other from sludge from a wastewater treatment plant (culture WWT-1), to use sulfate from PG was compared. In addition, the impact of this sulfate-rich waste in the microbial community was assessed. The highest efficiency in terms of sulfate reduction was observed with culture WWT-1. The bacterial composition of this culture was not significantly affected when sodium sulfate from the nutrient medium was replaced by PG as a sulfate source. Next generation sequencing (NGS) showed that this community was phylogenetically diverse, composed by bacteria affiliated to Clostridium, Arcobacter, and Sulfurospirillum genera and by SRB belonging to Desulfovibrio, Desulfomicrobium, and Desulfobulbus genera. In contrast, the bacterial structure of the community enriched from PG was modified when sodium sulfate was replaced by PG as the sulfate source. This culture, which showed the poorest performance in the use of sulfate from PG, was mainly composed by SRB related to Desulfosporosinus genus. The present work provides new information regarding the phylogenetic characterization of anaerobic bacterial communities with the ability to use PG as sulfate donor, thus, contributing to improve the knowledge of microorganisms suitable to be used in PG bioremediation. Additionally, this paper demonstrates that an alternative to lactate and low-cost carbon source (wine wastes) can be used efficiently for that purpose.