Percorrer por autor "Guedes, Mafalda"
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- Limestone processing sludge: from waste to sustainable resourcePublication . Guedes, Mafalda; Carrasqueira, Joana; Seixas, Tomás; Afonso, Clélia; Gil, Maria Manuel; Bernardino, Raul; Gamboa, Roberto; Bernardino, SusanaThe limestone quarrying and processing industry generates huge amounts of waste, with limestone sludge being one of the most prevalent and challenging by-products. This study aims to evaluate the potential of limestone sludge as a sustainable secondary raw material for the mechanochemical synthesis of bioceramics, specifically hydroxyapatite (HA), for high-added-value applications in bone tissue engineering. High-energy milling is innovatively used as the processing route: dry sludge (functioning as the calcium source), a phosphate source, and water were milled with the aim of producing calcium phosphates (in particular, hydroxyapatite) via mechanosynthesis. The industrial sludge was thoroughly analyzed for chemical composition, heavy metals, and mineral phases to ensure suitability for biomedical applications. The mixture of reagents was tailored to comply with Ca/P = 1.67 molar ratio. Milling was carried out at room temperature; the milling velocity was 600 rpm, and milling time ranged from 5 to 650 min. Characterization by XRD, Raman spectroscopy, and SEM confirmed the progressive transformation of calcite into hydroxyapatite through a metastable DCPD intermediate, following logarithmic reaction kinetics. The resulting powders are fine, homogeneous, and phase-pure, demonstrating that mechanosynthesis provides a low-cost and environmentally friendly pathway to convert limestone waste into functional bioceramic materials. This suggests that Moleanos sludge is a viable and sustainable source to produce tailored calcium phosphates and confirms mechanosynthesis as a cost-effective and reliable technology to activate the low-kinetics chemical reactions in the CaCO3-H3PO4–H2O system. This work highlights a novel circular economy approach for the valorization of industrial limestone sludge, turning a difficult waste stream into a high-value, sustainable resource.
- Physical, chemical and mineralogical properties of fine recycled aggregates made from concrete wastePublication . Evangelista, Luis; Guedes, Mafalda; De Brito, Jorge; Ferro, Alberto C.; Pereira, M. F.This paper assesses the physical, chemical and mineralogical characteristics of fine recycled aggregates obtained from crushed concrete waste, comparing them with two types of natural fine aggregates from different origins. A commercial concrete was jaw crushed, and the effect of different aperture sizes on the particle size distribution of the resulting aggregates was evaluated. The density and water absorption of the recycled aggregates was determined and a model for predicting water absorption over time is proposed. Both natural and recycled aggregates were characterized regarding bulk density and fines content. Recycled aggregates were additionally characterized by XRD, SEM/EDS and DTA/TG of individual size fractions. The results show that natural and recycled fine aggregates have very different characteristics. This should be considered in potential applications, both in terms of the limits for replacing amounts and of the rules and design criteria of the manufactured products. (C) 2015 Elsevier Ltd. All rights reserved.
- Reaction path in the mechanosynthesis of calcium phosphates using a biogenic calcium sourcePublication . Ferro, Alberto C.; Seixas, Tomás; Guedes, MafaldaCalcium phosphates were produced by mechanosynthesis, using eggshell, H3PO4 and 6-83 wt%-H2O. Mixtures were milled at 600 rpm during 0.5-12 h. Resulting calcium phosphates occur within specific milling domains; H2O concentration determines onset and stability of monophasic hydroxyapatite. Within the tested conditions, brushite is the first detected calcium phosphate precipitated from solution. In 6, 40 and 56 wt%-H2O, monetite intermediates brushite's transformation to hydroxyapatite; in 71 and 83 wt%-H2O transformation is direct. Hydroxyapatite formation is favoured at the H2O extremes tested, 6 and 83 wt%. CO2 build-up in the confined jar and nucleation-and-growth events during drying are possible obstacles upon control of morphology and composition of synthesised particles. The potential of chicken eggshell as direct biogenic source and the ability of high-energy milling as corresponding processing route to produce calcium phosphates was demonstrated. This signals a route for reliable production of brushite, monetite and hydroxyapatite. A preliminary milling map was built, allowing to obtain desired final product under specific milling conditions.