Materials Science Forum Vols. 514-516

Abstract: Al-rich sludge produced from industrial anodising and surface treatment processes had been tested in the fabrication of mullite-based materials, by using unidirectional dry pressing as shaping technique. Mixture with common natural silica and magnesium-containing materials, like ball clay, kaolin and diatomite were prepared in order to achieve interesting final fired refractory and/or electrical insulating materials. Microstructural changes upon sintering and crystalline phase evolution are detailed and their relationship with the electrical behaviour is also studied, by the use of impedance spectroscopy. Finally, different models were used to fit the experimental electrical resistivity values and to estimate the percolation limit of the bi-phase material.

Abstract: The recycling of wastes is nowadays a priority in terms of the EU policies. This study aims at the replacement of a certain percentage of clay (natural raw material) by residues produced in a municipal solid waste incineration (MSWI) process referred as Air Pollution Control (APC) residues. The main objective of this work concerns the prediction of the quantity of the waste that can be valorized as lightweight aggregates (LWA). For this analysis the Riley diagram was considered, which consists in plotting the percentage concentration of the main oxides (SiO2, Al2O3, fluxing) in a ternary diagram. The fluxing is defined as the sum of Fe2O3+CaO+MgO+Na2O+K2O. Our results point out that no more than 5% of APC residues should be considered, since the main oxide composition of APC residues is far away from bloating area. A pre-washing treatment improved the waste characteristics being then possible to increase the amount of residue that can be incorporated in percentages below 10%. This theoretical analysis can save experimental work, since it allows the prediction of the maximum amount of wastes to be tested.

Abstract: This paper is mainly focused on the characterisation of a glass material (GM) obtained from the thermal treatment of a bottom ash (BA) produced at the Municipal Solid Waste (MSW) incineration plant of Valorsul. By melting the BA at 1400°C during 2 hours, and without using any chemical additives, a homogeneous black-coloured glass was obtained. The thermal and mechanical properties of this glass were characterised. The thermal expansion coefficient, measured by dilatometry, was 9-10 x 10-6 per °C and the modulus of rupture, determined by four-point bending test, was 75±6 MPa, which are similar values to those exhibited by commercial soda-lime-silica glasses used in structural applications. The chemical and the ecotoxicological leaching behaviour of the GM were also analysed. The GM was submitted to a leaching procedure composed of 15 sequential extraction cycles. A liquid/solid (L/S) ratio of 2 l/kg was applied in each cycle. The leachates were filtered through a membrane of PTFE (porosity: 0.45 8m). The filtered leachates were characterised for different chemical parameters and for an ecotoxicological indicator (bacterium Vibrio fischeri). The GM was also submitted to a microwave acidic digestion for the assessment of the total metal content. The crude BA was also submitted to the same experimental procedures. The GM showed levels of chemical emission and ecotoxicity for V. fischeri much lower than those determined for the crude BA. Similar characterisation studies will be pursued with the glass-ceramics produced by adequate thermal treatment of the glass, in order to investigate the effect of the crystallization on the final properties.

Abstract: The aim of this work was to study a new procedure for the regeneration of activated carbon saturated with phenol. The study was accomplished in two steps: extraction of the pollutant with supercritical water at 410 °C and 275 bar, and gasification of phenol with supercritical water at temperatures ranging between 600 - 650 °C. It was observed that the regeneration process was very rapid and effective. The regenerated activated carbon always recovered its original adsorption capacity, even after several regeneration cycles. The gasification of phenol afforded CO2 and H2O, with a very fast first-order kinetic process. The activation energy was very low (0.192 kJ mol-1).

Abstract: Domestic-type batteries sample was tested aiming at its characterization and the evaluation of the feasibility of physical separation of its main components. The sample was essentially constituted by saline and alkaline types (Zn-MnO2 based systems, >90% w/w) and cylindrical shape (> 90% w/w). The mass balance of alkaline battery samples indicated as main battery components the steel case materials (25 %), the electrodes (71%) and the connector and separator/insulating materials (4 %), while the corresponding values to the saline type are 16%, 72% and 12% respectively. Despite electrochemical principles are similar, internal constitution of saline and alkaline batteries is different. Differences in electrolytes are also relevant (KOH in alkaline type and chloride salts in saline type) affecting therefore the mass balances in the chemical treatment. Fragmentation of batteries was done aiming at to evaluate the efficiency of the liberation of different components, namely scrap and electrodes. Results obtained are very promising considering the good efficiency reached on the physical separation treatment and consequently the chemical step will be necessarily improved.

Abstract: Plastic material is not easily biodegradable even after a long period, in fact a wide variety of waste materials can be utilized as inert in matrix cement. In this paper we have focused the attention on the use of plastic material particles incorporated as aggregate in concrete and we have evaluated the chemical, physical and mechanical properties