Materials Science Forum Vols. 587-588

Abstract: Sludges generated in leather tanning processing are very complex wastes with potential deleterious effect on the environment and its management constitutes a high cost for the companies. In this work, sludges from a Portuguese tanning company were characterized and leached with acid solutions in order to evaluate the metals removal yields. The sludges contain, as main metals, 15% Ca, 5% Fe and 2.2 % Cr, in a dry basis. Other minor elements namely Al, Ti, Zn, Pb and Cu were also detected. The leaching experiments were carried out with two types of acids – hydrochloric and sulfuric – and the effects of the reaction time, temperature and leachant concentration were evaluated. The reaction conditions strongly affected the chromium leaching yields, being temperature and acid concentration highly significant (confidence level above 99.9%). About 90% of Cr was leached using the higher levels of the factors (4h, 80°C and 2M H+, with both acids). Concerning the other major metals, iron leaching was very efficient (yields usually above 90%) whatever the conditions tested while calcium behaviour was quite different, depending on the type of acid used for the same H+ concentration: H2SO4 leaching efficiency was generally lower than HCl, probably due to the formation of less soluble calcium sulfate. The maximum calcium removal achieved was near 75%. The leaching process developed can be useful not only as a decontamination step of the tanning sludges, but also as a process for metals recovery to be potentially applied in an integrated recycling system, where several metal wastes from different sources could be processed.

Abstract: The hydrometallurgical processing of metal bearing residues is one of the established routes envisaging metals recovery. In these processes, the leaching operation plays a central role as allows the solubilization of metals for further separation and recovery as pure products. This route can be applied to spent domestic batteries recycling, which studies on sulphuric acid leaching of spent alkaline batteries are reported in this paper. Material samples used in the trials were prepared concerning the real proportion of the most common sizes and shapes of batteries found in the usual stream of this type of wastes. The research involved the evaluation of some factors which affect leaching yields namely temperature, reaction time and stirring speed, through a two-level factorial design methodology and analysis of variance. In this study, other factors related with leachant concentration and stoichiometry were maintained constant. Zinc leaching yields were generally high and even near 100% when the high levels of the variables were used, meaning that zinc oxides present in the electrodes are very reactive to acid leachant. The variables had all positive effects being temperature the most significant factor (confidence level 99%) while the other factors were less significant (98.8% for time and 95% for stirring speed). Concerning manganese, leaching yields obtained were more dependent from the factors, being also positive and varying from 11% (for low levels of factors combination) to 89% (for high levels of factors combination). Temperature and time were highly significant (confidence levels above 99.9%) while stirring speed was less significant (97%). Contamination of leach liquors with iron was also evaluated since it is an impurity which requires special attention during the process development. For the higher levels of the factors (t = 1 h, T=80°C and ω=400 rpm) the final solution contained 10 g/L Zn, 15 g/L Mn and 3.2 g/L Fe. The removal of the iron from the solution is a necessary step prior to the separation and recovery of zinc and manganese.

Abstract: The use of Al mineral salts in wastewater treatment is a well known process and most common [1]. For a long time we have been studying the feasibility of the aluminium anodizing waste as coagulant. In previous works, we have tested anodizing sludges in the treatment of municipal wastewaters and of paint industry wastewater in batch processes [2]. In this study we have tested the use of the aluminium anodizing waste as coagulant for the treatment of municipal wastewaters in continuous processes. Different muds from nine different anodizing facilities were collected and prepared for use as coagulant. In addition, two mud mixtures were prepared to study the influence of the combination of different muds in the efficiency of the treatment. The tests were made, being controlled important parameters such as pH, turbidity and chemical oxygen demand (COD). We have verified that the coagulation process was effective for all the muds and mixtures tested. The formation of flocs that settle rapidly was visible and the Turbidity and COD reduction obtained has demonstrated the efficiency of the anodizing mud as coagulant. Aluminium anodizing plants generate a large quantity of wastes that are a burden to the industry. This works regards the reuse of anodizing sludges in wastewater treatment.

Abstract: Brazil has one of the world’s most important Bauxite deposits, the raw material for the aluminium extraction metallurgy. This work is focused on finding a suitable application for the white dross residue (WDR), a second-generation waste material produced during the metal recovery from the slag left after the primary extraction of aluminium from the ore. A commercial lime-silica based glass frit was used, to which WDR additions were made (up to 30 wt.%), aimed at studying the devitrification process of the glasses produced. Such mixtures were melted at temperatures varying from 1100 to 1500°C and the resulting fritted glasses were heat treated at 900°C. The starting materials and the mixtures thereof were characterized before and after thermal treatment by differential thermal analysis, X-ray diffraction and fluorescence, and scanning electron microscopy. The results obtained showed that the WDR is easily incorporated into the glass matrix and causes easy devitrification after short heat treatment periods at low temperature.

Abstract: The main purpose of the present study is to assess the usefulness of filter cartridges from end-of-life biological and chemical protection masks, for other applications (with increased added value) instead of landfill deposition. Filters with different ages up to fifty years, were dismantled and divided in their components. Physico-chemical characterisation of each filter cartridge component was performed using different techniques such as: optical microscopy, Fourier transform infrared spectroscopy, pyrolysis, particle size distribution by laser diffraction, surface area determination from the nitrogen adsorption isotherms at 77K, determination of open porosity by helium pycnometry, and dynamic mechanical thermal analysis in the temperature range from -100°C to 200°C. It is shown that the loss of resilience of the rubber sealant is the main factor that controls the shelf life of filter cartridges. On the other hand, most of the charcoal in the activated carbon cloth remains active and can be useful for other less severe applications such as the removal of dissolved components from freshwater and/or marine systems.

Abstract: In Italy, the amount of thermoplastic materials is 5 million tons. The recovery is necessary through simple processes with high efficiency. The aim of this paper is to study the use of plastic material particles in the ceramic industry for the production of light bricks, since this waste burns during firing at high temperature. The clay is extracted by disused quarry of South Italy and the PVC is a by-product of polymeric bars production (San Giovanni in Fiore- Calabria). The clay and the PVC waste were characterised by thermal analysis, X-ray diffraction to identify the crystalline phases of raw material and EDS analyses to determine the chemical composition. Mixtures containing waste and clay materials were formed by extrusion and fired in a furnace using range temperatures of 900°C-1100°C. The obtained final products are bricks of 15 cm of length, 2 cm of thickness and 1.2 cm of height. The physical and mechanical properties were studied. These properties are used to define process firing temperature. Water absorption and linear shrinkage tests carried out as a function of the firing temperature.

Abstract: The possibility of using fly ash and shale as alternative raw materials for the production of structural ceramics was investigated. Fly ash is a by-product from coal-burning power plants, and shale is a sedimentary rock that if ground finely enough can exhibit a clay-like plasticity. Ceramic samples containing 10-50 wt% fly ash were formed from mechanical mixing of both kinds of powders that were packed and sintered in the temperature range 950-1200°C. It was verified that powders with larger fly ash content exhibited lower packing density resulting in compacts with a lower sintered density. Although an increase in fly ash content was associated to a larger presence of porosity in the sintered samples, as confirmed by microstructural analysis, all studied compositions when sintered at the highest temperatures exhibited satisfactory values for water absorption (< 10%), for flexural strength (20-64 MPa) and for hardness (20-30 GPa) indicating that they have potential to be applied in the production of structural ceramics.

Abstract: Photoactive films consisting of pure anatase, brookite or rutile were deposited on glass slides by a dip coating process from water dispersions or solutions obtained by using TiCl4 as the precursor. The films were characterized by X-ray diffraction, scanning electron microscopy and atomic force microscopy. The photocatalytic activity of the various samples was evaluated by using the photooxidation of 2-propanol in gas solid regime as probe reaction. Brookite and anatase films showed a good photoactivity degrading the substrate and the propanone produced during the reaction.

Abstract: Surface analysis techniques (XPS and grazing incidence X-ray diffraction GIXRD) and electrochemical techniques have been combined to elucidate the effect resulting from Cr+ and N+ co-implantation in the formation and evolution of passive layers generated on two different stainless steels (AISI 430 and AISI 304L) in alkaline medium. The results show that the nitrides formed on AISI 430, identified as (Cr,Fe)2N1-x, are less resistant to dissolution while the nitride phase formed in AISI 304L, NCr with nanocrystalline structure, allows the compact growth of the oxide film.

Abstract: In this work we studied the production of activated carbon fibres in monolith shape from a commercial textile acrylic fibre. The monoliths were produced with and without a binder. The binders tested were phenolic resin, polystyrene, polymethylmethacrylate and clay. We also tested the influence of using a solvent. The SEM analysis indicates that the monoliths are made of filaments that can be considered activated carbon fibres. The type of binder influences the fibre orientation, degradation and materials shrinkage, the worst results being obtained from the use of polymethylmethacrylate and polystyrene in toluene. The best results are obtained when the monoliths were produced only with acrylic fibre and with phenolic resin as binder. The use of solvents has opposite effects for the carbonised and activated samples. In the former case it seems that the water can be fibre protective but during activation the presence of water leads to an increase in the monolith’s burn-off. The methodology used leads to the formation of excellent samples for performing the gas separations O2/N2 and CO2/CH4. Some samples show maximum selectivity for the referred separations because N2 and CH4 are almost totally excluded from the porous structure which indicates a good potential to be utilised in PSA systems or for natural gas purification. The adsorption capacity is very dependent on the conditions used. Nevertheless, the best sample has a considerably high adsorption capacity (32cm3g-1 for CO2 and 4cm3g-1 for O2, after 200s contact time).