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- 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.
- Fermentation of biomass-derived syngas to ethanol and acetate by clostridium ljungdahliiPublication . Ortigueira, Joana; Pinto, Filomena; Gírio, Francisco; Moura, PatríciaIn the biochemical pathway of lignocellulosics conversion into fuels, a significant portion of biomass cannot be hydrolysed to fermentable sugars and remains as waste substrate that, due to its recalcitrance, is not converted to ethanol by microorganisms. In terms of product yield, this residual biomass represents renewable feedstock that is being wasted, which contradicts the target of 100% feedstock utilisation. The gasification of this biomass constitutes an alternative to circumvent this problem, as the produced synthesis gas (syngas) can be used as substrate for microorganisms that are able to convert CO, CO2 and H2 into important bulk chemicals and biofuels, such as ethanol, acetate and butanol [1,2]. Thus, syngas fermentation to ethanol and acetate can be regarded as a possible process to increase the overall product yield from lignocellulosic feedstock. Some advantages of fuels and chemicals production through syngas fermentation over metal catalyst conversion are the possibility of utilisation of the whole biomass regardless its quality, the independence of a fixed H2:CO ratio for the bioconversion process, a higher specificity of the microbial biocatalyst over chemical catalysts, and the bioreactor operation at ambient conditions [3]. However, syngas fermentation also presents several limitations, such as low yields and poor solubility of the gaseous substrate in the liquid phase. The objective of the present study was to evaluate C. ljungdahlii as microbial catalyst capable of fermenting syngas produced by gasification of spent solids obtained after lignocellulosic biomass saccharification and fermentation into ethanol. The heterotrophic and autotrophic growth of C. ljungdahlii were compared. Parameters such as bacterial growth, acetate and ethanol production, substrate consumption, and bioconversion yields were evaluated. In order to overcome the problem of gas diffusion in the liquid phase, fermentations were conducted at different total pressures
- Cork boiling wastewater management by anaerobic digestionPublication . Gonçalves, M. R.; Gil, Luís; Marques, Isabel PaulaCork boiling wastewater (CBW) is an aqueous and complex effluent of the cork industry which is produced during the boiling of the cork planks, one of the key operations in cork processing for cork stoppers production. CBW contains suspended and dissolved solids and organic materials such as phenolic compounds and is characterized by a low biodegradability and an acid pH. This boiling wastewater has no utility, being a serious environmental hazard. Anaerobic digestion is a promising technology for the treatment of organic effluents and for the simultaneous recovery of its energetic potential through methane production. Its application to cork effluents has never been subject of research. An anaerobic assay was conducted in order to determine the gas potential and biodegradability of the substrate using a mesophilic anaerobic consortium. Biodegradability batch experiments were performed at CBW concentrations of 3 and 6 kg COD m-3. The cork industry effluent was characterized (COD = 6.5 kg m-3; pH = 5.8). The liquid phase was analysed at the end of the experiment (pH, COD, total phenols). The methane accumulated in the vessels headspace was measured by gas chromatography. The maximum methane production was achieved after 15 days of experiment, and maintained until the end (44 days). The resultant methane potentials were 0.126 - 0.142 m3 CH4 kg-1 COD. The results suggest that CBW could be an interesting substrate for the anaerobic digestion process. The highest concentration (6 kg COD m-3) did not inhibit or significantly influenced the methane production. Concluding, a novel approach for the treatment and valorisation of the cork boiling effluent was revealed. The results demonstrate that the effluent from cork boiling can be treated and valorised by anaerobic digestion.
- Production and characterisation of amorphous silica from rice husk wastePublication . Madrid, Rosario; Nogueira, Carlos; Margarido, F.Rice covers about 1% of the earth’s surface. Rice husk is the major by-product of the riceprocessing industries which must be appropriately managed. On average 20% of the rice paddy is husk. The major constituents of rice husk are cellulose, lignin and silica. During growth, rice plants absorb silica and other minerals from the soil and accumulate it into their structures. Its composition varies with the diversity, climate and geographic location of growth. The high grade of silica in the husk opens a possibility for its valorisation. Through thermal treatment by calcination, with or without energy recovery, the ash obtained is constituted by amorphous silica with high porosity having potential application as ligand in construction materials, catalyst support, metals adsorbent, insulation or ceramics, among others. In the research developed, the rice husk was processed by washing, acid leaching and calcination in order to produce an ash, which was characterized aiming at assessing possible valorising solutions. The chemical treatment involved water washing for partial purification of the husk, and leaching with diluted sulphuric acid solution, allowing obtaining high metals removal efficiency, decreasing at least 90% of the initial content of contaminants (K, Fe and Mn). After calcination at 540ºC for organics decomposition, the final ash consisted in white colour amorphous silica as confirmed by XRPD analysis, being characterized by SEM to evaluate the microstructure. The results showed that after calcination the rice husk ash had a very porous, alveolar and even tracery morphology, which seems promising for applications requiring high reactivity, such as in construction materials and technical ceramics.
- Microalgae biomass as fermentation substrate for hydrogen and butyric acid production by clostridium tyrobutyricumPublication . Ortigueira, Joana; Lúcio, M.; Rodrigues, S.; Alves, Luís; Gouveia, Luisa; Moura, PatríciaFossil fuels are a limited type of feedstock, increasingly expensive, and carrying strong polluting properties. The search for alternative sources which can replace fossil fuels without the severe disadvantages that its use conveys is therefore of paramount importance. Microalgae biomass represents an example of such non-food renewable biomass that can be regarded as a valid alternative to fossil fuels. As biomass, microalgae are highly desirable since they are photosynthetic organisms with a very fast growth rate in comparison to higher plants, and their production does not require arable land or potable water. Furthermore, some microalgae are able to store large amounts of oil or sugars, prime materials for the production of biofuels and bulk-chemicals [1]. Scenedesmus obliquus is a microalgae with the referred properties, easily produced at large scale and capable of storing a high amount of sugars under nitrogen shortage. The objective of the present work was to investigate the production of hydrogen and butyrate from S. obliquus hidrolysate by four hydrogen- and butyrate-producing bacterial strains previously isolated by us and identified as Clostridium tyrobutyricum 1T, 2T, 3T and 9P. S. obliquus biomass was produced locally in air-lifts. After harvest, all biomass was submitted to acid pre-treatment [2] resulting in a microalgae hydrolysate with a final concentration of 10.3 g/l of glucose, xylose, arabinose, mannose and galactose. The hydrolysate was used as carbon and energy source for hydrogen and butyrate production by the four C. tyrobutyricum isolates. Hydrogen yields ranged from 0.63, 1.29, 1.36 and 1.24 of mol H2/ mol sugars by strains 1T, 2T, 3T and 9P, respectively. Hydrogen production was accompanied by the production of carbon dioxide and organic acids, mainly butyrate. Butyrate yields were 0.29, 0.49 and 0.48 mol butyric acid/ mol sugars, respectively by C. tyrobutyricum strains 1T, 2T and 3T, and 9P. The best C. tyrobutyricum isolate for combined hydrogen and butyrate production from S. obliquus hydrolysate will be used in further studies of energetic valorisation of spent algal biomass available from both biodiesel and bioethanol processes.