Browsing by Author "Almeida, Agostinho A."
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- Chemical safety of children's play paints: Focus on selected heavy metalsPublication . Rebelo, Andreia; Pinto, Edgar; Vieira Da Silva, Manuela; Almeida, Agostinho A.Children's play paints are widely used as didactic products in preschool activities. Besides direct skin contact, a great risk of oral exposure exists during its normal and foreseeable use. Due to the ubiquitous nature of most metals, their presence as impurities in all products is recognized as unavoidable. However, the toxic potential of most of them requires that their levels are kept as low as possible. The present study aimed to assess the content of selected heavy metals (Pb, Cd, Cr, Co, Ni, Mn, Cu and Zn) in “artist paints” (n = 54) and “face paints” (n = 12) commonly used in preschool establishments and available at low cost stores. Determinations were carried out by GFAAS (for Pb, Cd, Co, Cr and Ni) and FAAS (for Mn, Cu and Zn). The levels obtained [mean ± SD (maximum)] were: 0.48 ± 0.44 (1.98) μg g− 1 for Pb; 0.04 ± 0.04 (0.30) μg g− 1 for Cd; 0.17 ± 0.20 (1.47) μg g− 1 for Co; 1.36 ± 2.18 (9.40) μg g− 1 for Cr; 0.63 ± 0.56 (3.10) μg g− 1 for Ni; 19.8 ± 88.2 (718) μg g− 1 for Mn; 108 ± 260 (1458) μg g− 1 for Cu; and 130 ± 564 (3478) μg g− 1 for Zn. A safety assessment considering the estimated potential exposure and health-based limits (tolerable daily intakes) was performed. Overall, the results showed no reasons for safety concerns regarding the studied elements.
- A simple, efficient and selective process for recycling La (and Al) from fluid cracking catalysts using an environmentally friendly strategyPublication . Sadeghi, S. Maryam; Jesus, João; Pinto, Edgar; Almeida, Agostinho A.; Soares, Helena M. V. M.Spent fluid cracking catalyst (FCC) is an abundant waste material derived from oil refining processes and notably characterized by its content in rare earth metals, such as cerium (Ce) and lanthanum (La). In this work, it was our main aim to develop a simple but effective flowsheet, based on a single acid assisted leaching step followed by two consecutive precipitation steps, for recovering La with high purity from the FCCs. Firstly, three (conventional, ultrasound- and microwave-assisted) leaching strategies were tested using two acids (sulphuric acid, H2SO4, and hydrochloric acid, HCl). Microwave-assisted leaching was revealed to be the most efficient [(99.4 ± 0.9)% of La] and fastest leached (1 cycle of 90 s) strategy using a lower concentration of acid (1 M HCl) and low liquid-solid ratio (L/S = 5). Subsequently, a sequential selective alkaline and oxalate precipitation was capable of producing an aluminium hydroxide with 88.7% of purity by increasing the pH up to 6 and a highly pure (99.7%) salt of lanthanum oxalate (which can be calcinated into a reusable lanthanum oxide) using a reduced oxalate concentration. The proposed process is independent of the initial Al concentration present in the hydrochloric acid FCCs leachates and widely applicable (for [La] > 0.04 M, complete La precipitation can be achieved regardless of its initial concentration using a molar [oxalate]/[La] ratio of 2). Moreover, it is significantly simpler and faster than existing methods and minimizes the consumption of energy and reagents to a bare minimum, with accompanying cost reduction and environmental benefits.