Development and testing of porous materials for metal recovery from wastewater

This thesis encompasses the experimental work conducted over the past three years, focusing on the development, characterization, and optimization of porous materials for the selective recovery of precious metals from industrial wastewater. The recovery of noble metals from industrial wastewater and electronic waste has become increasingly critical to ensure the sustainable use of these non-renewable resources. Industries such as jewellery manufacturing and electronics contribute significantly to the global demand. Gold, a noble metal with a wide range of applications, has played a significant role in human development. Due to its relative scarcity compared to common base metals and the growing needs of modern society, gold recycling has become an essential aspect of industrial processes and urban waste management. Various strategies have been developed for gold extraction, but a major challenge is the separation of gold from other precious metals that coexist in multi-metal catalysts, electronic devices, and wastewater. However, a wide range of separation methods employed to date (e.g. ion-exchange resins, selective precipitation, selective reduction), often require large amounts of organic solvents or hazardous chemicals and generate waste that must be carefully managed. An alternative solution is provided by a range of absorbent materials, since adsorption has proven to be a particularly effective method for metal recovery thanks to the cost-effectiveness, the environmentally friendly nature and the semplicity. This process involves mechanisms such as chemisorption, ion exchange, and diffusion through porous structures, which makes it highly versatile. In this work, we propose the use of Poly(Acrylamide-co-Acrylic Acid) hydrogels and cryogels containing 2-Hydroxyethyl Acrylate (HEA) and acrylic acid for the selective recovery of gold from complex mixtures containing noble metals such as Pd, Pt, Rh, Ru, and Ir. The study investigates various aspects of porous materials, focusing on the mechanisms of metal adsorption and the influence of composition and synthesis methods on the process.