ME - Comunicações em actas de encontros científicos internacionais
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- Lead bioremoval by cork residues as biosorbentPublication . Mota, Dora; Marques, Paula; Rosa, Maria Fernanda; Gil, Luís; Marques, Carlos PereiraThe intensification of industrial activity during the last few years has greatly contributed to the increase of heavy metals in the environment, mainly in the aquatic systems [1]. Conventional technologies traditionally used for the removal of heavy metals from aqueous solutions are expensive and inefficient at low metal concentrations [2]. Biosorption, which is a property of different types of biomass (biosorbents) to bind and concentrate heavy metals from even very dilute aqueous solutions, is one of the most promising technologies that can be used for this purpose [3]. The goal of this work was to study the bioremoval process of Pb(II) ions from aqueous dilute solutions by cork granulates (1-2 mm) from a Portuguese cork processing company. The effect of physico-chemical parameters such as initial metal solution, pH, biomass cork pre-treatments and initial metal and biosorbent concentrations on the metal removal efficiency were investigated. The maximum Pb(II) uptake capacity (Qmax) of cork biomass was also determined from the Langmuir isotherm. The results obtained showed that the optimum initial pH for Pb(II) removal was in the range 3-4, leading to removal yields of about 90-100% for initial metal concentrations of 10-100 mg/L. Cork biomass without treatment provided a higher removal yield (93%) than the biomass submitted to previous extraction with deionised water (80%), ethyl acetate (83%) and ethanol (88 %). The Langmuir model showed a very good correlation with experimental results (r2=0.995) and the Qmax was determined as being 5.3 mg Pb(II)/g cork. The optimisation of continuous bioremoval of Pb(II) (10 mg/L) from 25 L of influent, regarding metal uptake yield and volume of effluent containing a Pb(II) concentration 1 mg/L (MAV), was carried out by the factorial design methodology, leading to the establishment of the best operating conditions. In these conditions, two fixed bed-reactors (operational liquid volume of each reactor containing 20g of biosorbent=138 mL) running in sequential mode (feed flow rate - 590 mL/h) were more efficient (effluent volume with [Pb(II)] 1 mg/L=10 L) than one reactor alone (effluent volume with [Pb(II)] 1 mg/L=5 L). Finally, the chemical characterization in terms of CQO, TOC and phenolic compounds of the effluent before discharge showed that all values were lower than the ones allowed by environmental legislation.
- Novel hydrogen generator: storage based on metal hydridesPublication . Rangel, C. M.; Fernandes, Vitor; Slavkov, Y.; Bozukov, Latchezar N.A novel electrochemical system has been developed which integrates hydrogen production, storage and compression in only one device, at relatively low cost and high efficiency. The prototype comprises a six electrode cell assembly using an AB5 type metal hydride and Ni plates as counter electrodes, in a KOH solution. Metal hydride electrodes with chemical composition LaNi4.3Co0.4Al0.3 has been prepared by high frequency vacuum melting followed by high temperature annealing. X-Ray phase analysis showed typical hexagonal structure and no traces of other intermetallic compounds belonging to the La-Ni phase diagram. Thermodynamic study of the alloy has been performed in a Sieverts type apparatus produced by Labtech. Ltd. In the present prototype during charging, hydrogen is absorbed in the metal hydride and corresponding oxygen is conveyed out of the system. Conversely, in the case of discharging the hydrogen stored in the metal hydride it is released to an external H2 storage. Released hydrogen is delivered into the hydrogen storage up to a pressure of 15 bar. In this work, a compact unit integrating production, storage and compressing hydrogen is proposed as one device at relatively low cost and higher efficiency than a classical electrolyser. It is anticipated that the device will be integrated as a combined hydrogen generator in a stand alone system associated to a 1 kW fuel cell.
- Towards a competitive use of solar driers : a case study for the lumber industryPublication . Loureiro, David; Martins, Maria João; Santos, José António dos; Nogueira, António Júlio; Pestana, Luís Câmara; Costa, J. Cruz; Ramalho, ÁlvaroThe aim of this paper is to contribute to the discussion of the methodology that leads to a better systematization of the knowledge on solar drying. Based on a case study for the lumber industry, the options and solutions adopted will be reported, along with their evaluation criteria and existing or developed tools. The kilns have 50 m3 interior capacity and proved the capability to dry maritime pine 27 mm thick, from green to 12% moisture content in about 33 days. The performance of the drying process has a significant seasonal and weather dependence, so an interactive control system is essential in order to profit as much as possible from the favorable exterior conditions.
- Production of hydrogen by borohydride: in search of low cost non-noble efficient catalystPublication . Rangel, C. M.; Fernandes, Vitor; Silva, R. A.; Bonnetot, B.; Laversenne, L.; Buni, A.; Minkina, V.; Perrin, J.Hydrogen production by sodium borohydride through hydrolysis in alkaline solutions has been extensively studied as a production/storage option due to the high volumetric and gravimetric efficiency exhibited. The potential application of this option is based on an easily controllable catalysed hydrolysis reaction, non-toxic and recyclable by-products, and the high purity hydrogen produced can be used in fuel cells. This work reports on a comparative study of own-developed, supported and non-supported, nonnoble catalyst. Ru based catalysts are taken as reference. Characterization of the catalyst was accomplished using a FEG-SEM scanning electron microscope and FTIR analysis. Obtained values amount to 10 NLmin-1g-1 for Ni-based catalyst while Ru-based catalyst amount to twice as much in the same experimental conditions. Typical solutions contain sodium borohydride of concentrations between 2 and 10 wt%, stabilized with 3 to 10 wt % NaOH. Produced hydrogen is measured at ambient pressure as a function of catalyst exposure time at controlled temperatures till completion of the reaction. A thorough study of the open literature rendered normalized values for the reaction rate with different catalyst, making comparisons valuable.
- Sintering response and mechanical properties of microwave sintered 316L Powder BlendsPublication . Mascarenhas, João; Marcelo, TeresaMicrowave sintering can be an efficient, economic and valuable approach for the processing of some PM materials. Recent findings on the ability of powdered metals to absorb and dissipate microwave radiation, opened new opportunities for the PM world. Being the particle size of the metallic powders one of the key parameters that rules the heating rate and the temperature performance during microwave sintering, work has been carried out on compacts of 316L powder blends with 60, 50, 25 and 7 m mean particle sizes, at 1150ºC for 30 minutes in a 2.45 GHz-1000 W microwave oven. Green and sintered densities and corresponding transverse rupture strength (TRS) are reported as well as hardness and porosity. Densities in excess of 95% were attained for the finer powders. TRS tests were performed on all but the 7 m powder specimens, being the highest value of 630 MPa obtained for the 25 m powder specimens
- Novel approach to plasma facing materials in nuclear fusion reactorsPublication . Livramento, Vanessa; Correia, J.B.; Nunes, D.; Carvalho, Patricia Almeida; Fernandes, H.; Silva, C.; Hanada, K.; Shohoji, Nobumitsu; Osawa, E.A novel material design in nuclear fusion reactors is proposed based on W-nDiamond nanostructured composites. Generally, a microstructure refined to the nanometer scale improves the mechanical strength due to modification of plasticity mechanisms. Moreover, highly specific grainboundary area raises the number of sites for annihilation of radiation induced defects. However, the low thermal stability of fine-grained and nanostructured materials demands the presence of particles at the grain boundaries that can delay coarsening by a pinning effect. As a result, the concept of a composite is promising in the field of nanostructured materials. The hardness of diamond renders nanodiamond dispersions excellent reinforcing and stabilization candidates and, in addition, diamond has extremely high thermal conductivity. Consequently, W-nDiamond nanocomposites are promising candidates for thermally stable first-wall materials. The proposed design involves the production of WAV-nDiamondAV-Cu/Cu layered castellations. The W, W-nDiamond and W-Cu layers are produced by mechanical alloying followed by a consolidation route that combines hot rolling with spark plasma sintering (SPS). Layer welding is achieved by spark plasma sintering. The present work describes the mechanical alloying processsing and consolidation route used to produce W-nDiamond composites, as well as microstructural features and mechanical properties of the material produced Long term plasma exposure experiments are planned at ISTTOK and at FTU (Frascati).
- Penetration of hydrogen technologies: study on the environmental impact of road transport in PortugalPublication . Travassos, Maria Antónia; Sá, A.I. De; Luz, Paulo P. da; Rangel, C. M.Road traffic is one of the transportation sectors with faster growth and also one of the most important emitters of greenhouse gases (GHGs). In this work, an analysis of the environmental benefits resulting from the introduction of hydrogen on road transport in Portugal is made. Impact is analyzed mainly looking at the pollutant emissions provided by road transport at the point of use. Emissions associated to road transport have been estimated using the software COPERT (version 4), since it provides a detailed methodology for each specific pollutant related to the vehicle fleet of a region or country, as well as the driving conditions and fuel consumption. Passenger cars, light duty vehicles and public transport buses are the vehicles categories in which the hydrogen technology is foreseen. The hydrogen penetration rates (moderate and high) are extracted from the European Project HYWAYS. Two trends are then considered, which give penetration rates of 40.0 % and 74.5 % in 2050 for the moderate and high scenarios respectively.
- Solar hydrogen production from aqueous solutions of ethanol at near ambient temperaturesPublication . Rangel, C. M.; Silva, R. A.; Fernandes, Vitor; Paiva Luís, TeresaNanostructured semi-conductor materials based on titanium dioxide, with effective photo-catalytic properties under UV illumination, were synthesized using sol-gel technology and characterized by X-Ray diffraction and scanning electron microscopy, with the objective of studying the photo-catalytic hydrogen production from water. The need to decrease the electron-hole recombination rate was accounted for by metal doping and the addition of ethanol as a hole trap. Aqueous suspensions of the semiconductor powders, with noble metal loadings (Pt) of 1.5 wt% were used and the effect of solution pH and temperature (20-70ºC) on hydrogen production were studied, for a selected catalyst concentration. Hydrogen production rates were found to be linear with solution temperature with values larger than published literature data.
- Metals recovery from spent Zn-MnO2 batteries by HydrometallurgyPublication . Nogueira, Carlos; Guerra, R. N. G.; Pedrosa, Fátima; Margarido, F.A hydrometallurgical process for recycling spent Zn-MnO2 batteries was developed, involving leaching with sulfuric acid, purification by precipitation and metals separation for further recovery. Leaching of zinc oxide was easily attained while for manganese oxide was rather difficult depending on temperature and acid concentration. At 90ºC and with the liquid/solid ratio of 20 L/kg, more than 95% of zinc is recovered in 30 minutes with 0.5M H2SO4. To attain similar recovery for manganese, higher levels of acid concentration and time are needed (e.g 0.7 M and 2 hours). After leaching a purification step is necessary to remove iron co-dissolved through Fe(III) precipitation. Separation of zinc from manganese by solvent extraction with 1M DEHPA follows in the process route. The countercurrent multistage separation diagram developed allows the production of a zinc electrolyte with 120 g/L Zn and 0.005 g/L Mn, and a raffinate with 16 g/L Mn and 0.013 g/L Zn.
- Physical processing efficiency of saline vs. alkaline spent batteriesPublication . Cabral, Marta; Nogueira, Carlos; Margarido, F.Physical processing of spent batteries which includes shredding and sieving operation is the first step for chemical treatment by hydrometallurgy. A laboratory study was carried out to evaluate physical processing efficiency, by analysing the resulting particle size, of alkaline and saline mignon-type Zn-MnO2 batteries. After shredding with a tip shredder, results obtained showed that alkaline batteries were more efficiently size reduced than saline batteries. Difference in particle size distribution was larger for granulometric fraction -20+11.2 mm and also higher for saline batteries. Average diameters (d50) for saline and alkaline batteries were respectively 9.1 and 6.2 mm. Chemical composition carried out on several granulometric fractions allowed to identify metals distribution through size categories. This analysis showed that zinc concentration with the grain size was almost constant, while manganese decreased when particle size increased. More than 95% of iron scarp from the battery cases had a particle size higher than 5.6 mm.