STUDIO E SVILUPPO DI PROCESSI IDROMETALLURGICI SOSTENIBILI PER IL RECUPERO DI METALLI PREZIOSI DA RIFIUTI DI APPARECCHIATURE ELETTRICHE ED ELETTRONICHE

In this particular historical period where technology goes hand in hand with human activity, one issue of paramount importance is the management of waste electrical and electronic equipment, so-called WEEE. Correct disposal of WEEE leads first and foremost to an environmental benefit. In addition, valuable materials and metals with enormous economic value can be extracted from such waste, which become secondary raw materials, entering the circular economy, according to the concept of Urban mining, i.e. from city waste. E-waste from the automotive sector is also part of this scenario and is for these reasons a valuable secondary source of critical raw materials. In this context, this thesis work consists of three distinct research strands, the common objective of which is the study and optimisation, by means of laboratory and pilot scale tests, of hydrometallurgical processes suitable for the treatment of three different types of materials, all of which can be ascribed to the electrical and electronic waste (WEEE) family and more specifically to the automotive sector. The process study was conducted from the UNIVAQ GoldREC-1 and GoldREC-2 patents. Based on a supply risk analysis, the following critical materials were selected: printed circuit boards of car dashboards, flexible printed circuit boards and indium tin oxide of liquid crystal displays. Within this study, a careful literature review was initially carried out, characterisation tests were then carried out to determine the intrinsic economic potential of each material. Subsequently, leaching, selective precipitation and electrodeposition tests were conducted to study hydrometallurgical processes aimed at recovering critical, precious and base metals. Then, the processes developed were optimised by means of factorial experimentation techniques and reuse of residual solutions with the aim of striving for Zero-Liquid-Discharge (ZLD) processes. To achieve these objectives, the titration of chemical reagents was carried out to determine their consumption and define their replenishment for countercurrent leaching and reuse of solutions in new treatment cycles. Some of these experiments were also conducted on a pilot scale at the hydrometallurgical plant reconfigured as part of the Treasure project. Based on the experimental results obtained, a process analysis was then carried out in which the material and energy balances were described. In order to confirm these results, and to assess the timing of operations (Gantt), a process simulation was conducted using the SuperPro Designer software. Finally, with the aim of assessing the economic sustainability of the process, operating costs (OpEx), investment costs (CapEx) and revenues were estimated.