TY: THES T1 - Recovery of platinum-group elements using a graphene nanocomposite A1 - Rocha, Filipe José Martins N2 - The Platinum group elements (PGE) consists in six metallic elements (Ru, Rh, Pd, Os, Ir and Pt), that due to their unique characteristics are widely used in many applications, such as catalysis. Their scarcity at the Earth?s crust, the complexity of the exploration and purification processes, the increasing worldwide demand and the growing environmental concern related with the exploration processes, have increase the importance of the recovery of these elements from leaching and waste solutions. Carbon-based sorbents have been widely used in water treatment due to their excellent physico-chemical properties, while magnetite (Fe3O4) nanoparticles (NPs) have been recognized by combine magnetic properties with efficiency in water treatment. Under this context, the preparation of hybrid structures that combine the properties of these two types of materials will allow the implementation of efficient magnetic separation technologies in water treatment units using sorption processes. In this work, two magnetic nanocomposites were synthetized by two different techniques, using exfoliated graphite (EG) and Fe3O4 NPs as precursors. EG was prepared by ultrasonic treatment of graphite powder, while Fe3O4 NPs were obtained by oxidative hydrolysis of FeSO4. The magnetic nanocomposite, denoted by Fe3O4@EG_01 was prepared by electrostatic assembly of EG and Fe3O4 NPs, while the magnetic nanocomposite Fe3O4@EG_02 was obtained by oxidative hydrolysis of FeSO4, in the presence of EG. The characterization of both materials revealed that the nanocomposites were successfully synthesized and combine properties of both precursors. The recovery of Pd, Pt, Ru, Rh and Ir (1 ?mol dm-3) was studied by carrying batch experiments using the nanocomposites and their precursors, in spring water and varying different parameters (pH, sorbent dose and contact time). The sorption results shown different patterns, which allow to group the elements in three groups (Pt and Ir, Pd and Ru and Rh). The highest values of PGE removal efficiencies were achieved at pH 7 for Fe3O4@EG_02. The kinetic results for Pd and Ru were well fitted by the pseudo-second order model (R2>0.960; Sy.x<0.713), while the Elovich model was the most suitable for the Rh sorption (R2>0.972; Sy.x<0.677). From all the equilibrium models tested, the Freundlich model was the one that better fitted the equilibrium data for Pd, Ru and Rh (R2>0.838). This study highlights that is possible to effectively recover some PGE, even from low-concentration solutions UR - https://ria.ua.pt/handle/10773/25537 Y1 - 2018 PB - No publisher defined