Removal of elements with high economic and technological value from complex aqueous mixtures by living marine macroalgae

• Autor(a) principal: Ferreira, Thainara Viana
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/31960
• topic: Living marine macroalgae; Complex mixtures of contaminants; Removal and recovery; Critical elements; Response sureface methodology; Box-Behnken design

Human activity and survival as biodiversity depends on aquatic systems that, unfortunately, have been directly and indirectly threatened by anthropogenic actions, strongly contributing to the loss of water quality. Electronic waste (e-waste) is one of the most ascending waste streams, whose management has become a priority to avoid environmental impacts, such water contamination. At the same time, e-waste is a rich source of elements of high economic and technological interest such as gold, silver, copper, lithium, cobalt, platinum group elements, and rare earth metals, which can be recovered and re- introduced into the production cycle. The use of macroalgae as a biosorbent has gained focus as it can be considered a simple, economical and eco-friendly solution for contaminated water treatment. However, this process still faces some challenges, and most published articles are limited to evaluate the removal of one or a few elements from a single group, contrasting with the composition of real industrial effluents, and do not include process optimization. This means that there are still few commercially available biosorbents on the market. The main objective of the present work is to evaluate and optimize parameters that influence the efficiency of the biosorption/bioaccumulation process performed by a live marine macroalgae (Ulva lactuca), in a complex mixture of contaminants that simulates an effluent from a lamp industry, following the Response Surface Methodology (RSM) with a Box-Behnken Design. The results of the controls experiments pointed to the inexistence of losses or contaminations during the experiments, and the analysis of the central point of the Box-Behnken confirmed the reproducibility of the methodology. Based on the statistical treatment of the data, for a significance level of 0.05 (ANOVA), the factor with the greatest impact on the removal of elements revealed to be the initial macroalgae dosage, with higher values allowing for greater removals (up to 88 % in 24 h, for rare earth elements (REEs)). The conditions determined as optimal for the removal of REEs were: initial concentration of 10 μg/L, at salinity 10, and using 5.0 g/L of macroalgae. Through the cell partition of the sorbed elements, via selective extractions with EDTA, it was found that most of them were located on the external surface of U. lactuca. On the contrary, the Hg was accumulated internally and Co, Pt and Ce were distributed between the two fractions.