Maria Clara Costa

Wine wastes as carbon source for biological treatment of acid mine drainage

Possible use of wine wastes containing ethanol as carbon and energy source for sulphate-reducing bacteria (SRB) growth and activity in the treatment of acid mine drainage (AMD) is studied for the first time. The experiments were performed using anaerobic down-flow packed bed reactors in semi-continuous systems. The performance of two bioreactors fed with wine wastes or ethanol as carbon sources is compared in terms of sulphate reduction, metals removal and neutralization. The results show that efficient neutralization and high sulphate removal (>90%) were attained with the use of wine wastes as substrate allowing the production of effluents with concentrations below the required local legislation for irrigation waters. This is only possible provided that the AMD and wine wastes are contacted with calcite tailing, a waste material that neutralizes and provides buffer capacity to the medium. The removal of metals using wine wastes as carbon source was 61-91% for Fe and 97% for both Zn and Cu. The lower removal of iron, when wine waste is used instead of ethanol, may be due to the presence of iron-chelating compounds in the waste, which prevent the formation of iron sulphide, and partial unavailability of sulphide because of re-oxidation to elemental sulphur. However, that did not affect significantly the quality of the effluent for irrigation. This work demonstrates that wine wastes are a potential alternative to traditional SRB substrates. This finding has direct implication to sustainable operation of SRB bioreactors for AMD treatment.

Anaerobic bio-removal of uranium (VI) and chromium (VI): Comparison of microbial community structure

Several microbial communities, obtained from uranium contaminated and non-contaminated samples, were investigated for their ability to remove uranium (VI) and the cultures capable for this removal were further assessed on their efficiency for chromium (VI) removal. The highest efficiency for removal of both metals was observed on a consortium from a non-contaminated soil collected in Monchique thermal place, which was capable to remove 91% of 22 mg L(-1) U(VI) and 99% of 13 mg L(-1) Cr(VI). This study revealed that uranium (VI) removing communities have also ability to remove chromium (VI), but when uranium (VI) was replaced by chromium (VI) several differences in the structure of all bacterial communities were observed. TGGE and phylogenetic analysis of 16S rRNA gene showed that the uranium (VI) removing bacterial consortia are mainly composed by members of Rhodocyclaceae family and Clostridium genus. On the other hand, bacteria from Enterobacteriaceae family were detected in the community with ability for chromium (VI) removal. The existence of members of Enterobacteriaceae and Rhodocyclaceae families never reported as chromium or uranium removing bacteria, respectively, is also a relevant finding, encouraging the exploitation of microorganisms with new abilities that can be useful for bioremediation.

Characterization of a natural and an electro-oxidized arsenopyrite: a study on electrochemical and X-ray photoelectron spectroscopy

This paper discusses the results of a detailed study on the electrochemistry of an arsenopyrite mineral and a concentrate as well as other mineral species contained in it in a chloride medium (NaCl 1.9 M+HCl 0.1 M) using cyclic voltammetry. The surface modification promoted by the anodic oxidation of arsenopyrite mineral samples (+0.8 V for 1 h) is also analysed. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy have been used to provide information on the chemical state of natural and electrooxidized surfaces. The results showed that layers of elemental sulphur are produced on the oxidized surface of arsenopyrite by the formation of an intermediate metal-deficient sulphide Fe1 � xAs1 � yS. Other surface oxidation products such as iron oxides, arsenic oxides and oxysulphur species have also been detected, confirming the interpretation of the voltammetric studies. The identified surface products show that arsenopyrite oxidation occurs by the diffusion of the metal atoms from the bulk to the interface region and by their interaction with air forming metal oxide layers (mainly iron and arsenic oxides) and leaving a predominant elemental sulphur layer.

Mechanism of uranium (VI) removal by two anaerobic bacterial communities.

The mechanism of uranium (VI) removal by two anaerobic bacterial consortia, recovered from an uncontaminated site (consortium A) and other from an uranium mine (consortium U), was investigated. The highest efficiency of U (VI) removal by both consortia (97%) occurred at room temperature and at pH 7.2. Furthermore, it was found that U (VI) removal by consortium A occurred by enzymatic reduction and bioaccumulation, while the enzymatic process was the only mechanism involved in metal removal by consortium U. FTIR analysis suggested that after U (VI) reduction, U (IV) could be bound to carboxyl, phosphate and amide groups of bacterial cells. Phylogenetic analysis of 16S rRNA showed that community A was mainly composed by bacteria closely related to Sporotalea genus and Rhodocyclaceae family, while community U was mainly composed by bacteria related to Clostridium genus and Rhodocyclaceae family.

Solvent Extraction of Iron(III) from Hydrochloric Acid Solutions Using N,N′‐Dimethyl‐N,N′‐diphenylmalonamide and N,N′‐Dimethyl‐N,N′‐diphenyltetradecylmalonamide

Abstract The use of N,N′‐tetrasubstituted malonamides such as N,N′‐dimethyl‐N,N′‐diphenylmalonamide (DMDPHMA) and N,N′‐dimethyl‐N,N′‐diphenyltetradecylmalonamide (DMDPHTDMA) for the extraction of iron(III) from acid chloride solutions is investigated, in order to evaluate the possibility of using this family of compounds to extract base metal cations. In the present work, a mechanism for iron(III) extraction from chloride media by DMDPHMA and DMDPHTDMA is proposed, a comparison between their extraction behavior and involved mechanisms for both chloride and nitrate media being considered as well. Hydrochloric acid extraction, slope analysis and spectroscopic data—IR, UV, and NMR—were used to acquire information on the iron(III) extraction reactions. The results suggest that DMDPHMA and DMDPHTDMA extract iron(III) through different mechanisms, thus showing the influence of the chemical structure on the metal ion transfer reactions to the organic phase. For DMDPHMA, an anionic‐pair mechanism involving iron(III) extraction as the chlorocomplex FeCl4 − seems to occur, while for DMDPHTDMA a solvation mechanism appears to be the predominant one. The stripping of iron(III) from the loaded organic phases is quantitatively achieved by a simple contact with water, and the selectivity towards iron(III) presented by both malonamide derivatives when several base metal cations co‐exist in the acid chloride aqueous solutions can be considered very promising.

Recovery of Platinum and Palladium from Chloride Solutions by a Thiodiglycolamide Derivative

The 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.

Effect of uranium (VI) on two sulphate-reducing bacteria cultures from a uranium mine site

This work was conducted to assess the impact of uranium (VI) on sulphate-reducing bacteria (SRB) communities obtained from environmental samples collected on the Portuguese uranium mining area of Urgeiriça. Culture U was obtained from a sediment, while culture W was obtained from sludge from the wetland of that mine. Temperature gradient gel electrophoresis (TGGE) was used to monitor community changes under uranium stress conditions. TGGE profiles of dsrB gene fragment demonstrated that the initial cultures were composed of SRB species affiliated with Desulfovibrio desulfuricans, Desulfovibrio vulgaris and Desulfomicrobium spp. (sample U), and by species related to D. desulfuricans (sample W). A drastic change in SRB communities was observed as a result of uranium (VI) exposure. Surprisingly, SRB were not detected in the uranium removal communities. Such findings emphasize the need of monitoring the dominant populations during bio-removal studies. TGGE and phylogenetic analysis of the 16S rRNA gene fragment revealed that the uranium removal consortia are composed by strains affiliated to Clostridium genus, Caulobacteraceae and Rhodocyclaceae families. Therefore, these communities can be attractive candidates for environmental biotechnological applications associated to uranium removal.

Solvent Extraction of Iron(III) from Acidic Chloride Media Using N,N′‐Dimethyl‐N,N′‐dibutylmalonamide

Abstract In the present paper, a new, simple, and effective method for iron(III) extraction from acidic chloride solutions is described involving the use of a N,N,N′,N′‐tetrasubstituted malonamide, N,N′‐dimethyl‐N,N′‐dibutylmalonamide (DMDBMA). The behavior of this ligand towards iron(III) extraction was investigated for different experimental conditions with a particular emphasis on the influence of HCl, LiCl, and ligand concentrations. The extraction behavior of DMDBMA is compared with the ones shown by two similar malonamide derivatives, N,N′‐dimethyl‐N,N′‐diphenylmalonamide (DMDPHMA) and N,N′‐dimethyl‐N,N′‐diphenyltetradecylmalonamide (DMDPHTDMA), previously studied. The mechanism involved on iron(III) extraction, the structure of the metal–adducts formed, and also the relationship between the extraction mechanism and the ligand structures are clarified. Therefore, hydrochloric acid extraction, slope analysis, and spectroscopic data—UV and NMR—were used to collect information on the iron(III) extraction reactions. A solvation mechanism involving iron(III) extraction as chlorocomplexes such as HFeCl4 and FeCl3 is proposed. From aqueous feed solutions with HCl concentrations higher than 4 M, iron(III) is mainly extracted as the anionic chlorocomplex, while from solutions with lower HCl concentrations (2 M < CHCl ≤ 4 M) the metal is probably removed as FeCl3. The results also suggest that different malonamides (e.g., DMDBMA, DMDPHMA, and DMDPHTDMA) extract iron(III) through diverse mechanisms, thus showing the important role played by the chemical structure on the metal ion transfer reactions to the organic phase. The efficient extraction of iron(III) from aqueous chloride solutions and the selectivity of the ligand for this metal ion when in the presence of interfering ions such as copper, zinc, nickel, cobalt, lead, and silver, in binary and in multicomponent mixtures, are also reported. The high selectivity towards iron(III), the complete stripping of this metal by simple contact of the loaded organic phase with water and the efficient reutilization of DMDBMA are very promising results that can justify an eventual industrial application.

The Solvent Extraction Performance of N,N’-Dimethyl-N,N’-Dibutylmalonamide Towards Platinum and Palladium in Chloride Media

The 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 0.1 M thiourea in 1 M HCl. 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.

Oxidative leaching process with cupric ion in hydrochloric acid media for recovery of Pd and Rh from spent catalytic converters

The 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 Cu(2+) 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 = 4h, [HCl] = 6M, [Cu(2+)] = 0.3M).