Recovery of rare earths from natural waters using carbon-based nanomaterials

• Autor(a) principal: Cardoso, Celso Eduardo Dias
• Data de Publicação: 2018
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/24228
• topic: E-waste; Graphene oxide; Magnetite; Rare earths elements; Recovery; Sorption; Humic acids; Polyethylenimine; Chitosan

The society has never been so much dependent on electronic and electric devices as it is today. As a result, e-waste has become a worldwide problem not only due to environmental changes that have emerge from the incorrect treatment and storage of e-waste but also because the amount of e-waste is increasing each year. Another problem inherent to electrical and electronic devices is their dependence on rare earth elements. Currently, they are considered as the “vitamins” of modern industry due to their vital role on the development of new cutting-edge technologies due to their distinctive chemical and physical properties. However, the high demand and the limited resources of rare earth elements, combined with the environmental problems associated with their exploration by mining activities, enforce the development of new ways to recover these elements from e-waste and wastewaters. Therefore, the development of low cost techniques and materials for recovery these valuable elements from e-waste is important to face and resolve both issues. In this way, the main objective of this work was to develop an efficient carbonbased composite towards the recovery of rare earths. Most of the sorption studies reported in the literature were performed with ultrapure waters spiked with tens to hundreds mg/L of single rare earth elements; so the objective is to study the recovery from waters of different matrices and using lower element concentrations. The materials synthesized in this work were magnetic exfoliated graphite functionalized with humic acids (MEG-HA), graphene oxide functionalized with ca. 25% of polyethylenimine (GO-PEI) and graphene oxide functionalized with chitosan (GO-CH), and they were evaluated for the REEs recovery capacity, using different amount of sorbent and in the presence of different type of waters. In ultrapure water, average recovery percentages of 47%, 97% and 71% were obtained using 100 mg/L of MEG-HA, GO-PEI and GO-CH, respectively. The sorption behaviour of the composites showed that the recovery is more efficient in mineral water, either using MEG-HA or GO-PEI, achieving recovery percentages around 100%. However, in saline water, the recovery percentages decrease to ca. 60 and 50% using 100 mg/L of GO-PEI and MEG-HA, respectively. The results were adjusts using kinetic models of pseudo first order, pseudo second order and Elovich and the sorption mechanism that better described the interaction between the nanocomposites and REEs was chemisorption. The application of the nanocomposites tested for the recovery of rare earth elements from aqueous solutions confirms that the carbon-based composites have a great potential to be used in the recovery of REEs