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Recovery of gold(0) nanoparticles from aqueous solutions using effluents from a bioremediation process

Publication . Assunção, Ana; Vieira, Bernardete; Lourenço, J. P.; Costa, Maria Clara

The 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.

2016Journal article

Open Access

Biological and chemical strategies for the recovery of precious and rare metals as nanoparticles

Publication . Assunção, Ana; Costa, Maria Clara

The 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.

2016-07-07Doctoral thesis

Open Access

Application of urea-agarose gel electrophoresis to select non-redundant 16S rRNAs for taxonomic studies: palladium(II) removal bacteria

Publication . Assunção, Ana; Costa, Maria Clara; Carlier, Jorge

The 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.

2016-07Journal article

Open Access

A bridge between liquid-liquid extraction and the use of bacterial communities for palladium and platinum recovery as nanosized metal sulphides

Publication . Assunção, Ana; Matos, Ana; Costa, Ana M. Rosa da; Candeias, Antonio; Costa, Maria Clara

The 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.

2016-08Journal article

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