Cobalt and tungsten are known to be critical, strategic materials for many productive fields, and their circular economy would reduce their costs and deployment of natural resources. This research carries on a previous work focused on the recover of Co and W from hardmetal (HM) scraps through electrochemical way using a neutral, mild and aqueous electrolyte. Current recycling methods are characterized by high energy consumption, carbon footprint and difficult chemical’s disposal. The main challenge is to overcome the pseudopassivating behaviour of this material through electrochemical demolition. This work is divided into three main topics: (i) understanding of hardmetal's electrochemical behaviour and analysis of critical potentials; (ii) optimization of the electrochemical demolition process to increase throughput and reduce energy consumption; (iii) microstructural and compositional analysis of the obtained compounds. A systematic investigation made through cyclic voltammetry (CV) allowed to detect critical potential and the different material’s behaviours by varying the anodic terminal voltage (ATV). Then, potentiostatic staircase (SPS) test allowed to determine the right potential at which OER develops at the boundary between subsurface residual electroactive region and the insulating film, mechanically breaking the inactive layer thanks to oxygen formation. Thanks to these informations was then possible to define a potentiostatic square wave (PSW) protocol to be applied in order to have a continuous extraction and surface-reactivation loops. The optimization of this protocol allowed an analysis of the efficiency of the developed method both in terms of throughput and energy consumption. Microstructural and compositional characterization then was necessary to identify the nature of the obtained compounds, defining the effectiveness of the overall process in terms of material extraction and components separation in order to reduce the required steps to obtain high purity grades of raw materials.
Cobalto e tungsteno sono noti per essere materiali strategici e critici in vari ambiti produttivi, e una loro economia circolare ridurrebbe i loro costi e lo sfruttamento di risorse naturali. Questa ricerca porta avanti un lavoro precedente focalizzato sul riciclo di Co e W da scarti di metallo duro tramite un metodo elettrochimico usando un elettrolita neutro e acquoso. I metodi di riciclo attuali sono caratterizzati da elevati consumi energetici, impronta carbonica e difficile smaltimento di prodotti e solventi chimici. La sfida principale è stato il superamento del comportamento pseudopassivante del metallo duro tramite una demolizione elettrochimica. Questo elaborato è suddiviso in tre macrosezioni: (i) analisi del comportamento elettrochimico del materiale e studio dei potenziali critici; (ii) ottimizzazione del processo di demolizione elettrochimica per aumentare la produzione e ridurre i consumi energetici; (iii) analisi microstrutturale e della composizione dei prodotti di processo. Un’analisi sistematica condotta tramite ciclovoltammetrie (CV) ha permesso di individuare i potenziali critici e i diversi comportamenti del materiale al variare del potenziale anodico (ATV). Quindi applicando una rampa di potenziali, è stato possibile determinare il potenziale in corrispondenza del quale ci fosse un giusto sviluppo di ossigeno nello strato limite tra l’area attiva residua e il film isolante, in modo da rompere meccanicamente la superficie passivante grazie allo sviluppo di ossigeno. Grazie a queste informazioni è stato quindi possibile definire il protocollo di una potenziostatica ad onda quadra (PSW) in modo da avere continui cicli di estrazione del materiale e riattivazione della superficie. L’ottimizzazione di questo protocollo ha quindi consentito un’analisi dell’efficienza del metodo sviluppato in termini di produttività e consumi energetici. La caratterizzazione microstrutturale e di composizione è stata quindi necessaria per identificare la natura dei prodotti di processo, definendo l’efficacia della demolizione in termini di materiale estratto e separazione dei componenti in modo da ridurre gli step necessari per ottenere sufficienti purezze dei prodotti finali.
High-throughput electrochemical demolition of grade Co12WC88 hardmetal scrap for Co recovery
BIDINOTTO, GIULIO
2022/2023
Abstract
Cobalt and tungsten are known to be critical, strategic materials for many productive fields, and their circular economy would reduce their costs and deployment of natural resources. This research carries on a previous work focused on the recover of Co and W from hardmetal (HM) scraps through electrochemical way using a neutral, mild and aqueous electrolyte. Current recycling methods are characterized by high energy consumption, carbon footprint and difficult chemical’s disposal. The main challenge is to overcome the pseudopassivating behaviour of this material through electrochemical demolition. This work is divided into three main topics: (i) understanding of hardmetal's electrochemical behaviour and analysis of critical potentials; (ii) optimization of the electrochemical demolition process to increase throughput and reduce energy consumption; (iii) microstructural and compositional analysis of the obtained compounds. A systematic investigation made through cyclic voltammetry (CV) allowed to detect critical potential and the different material’s behaviours by varying the anodic terminal voltage (ATV). Then, potentiostatic staircase (SPS) test allowed to determine the right potential at which OER develops at the boundary between subsurface residual electroactive region and the insulating film, mechanically breaking the inactive layer thanks to oxygen formation. Thanks to these informations was then possible to define a potentiostatic square wave (PSW) protocol to be applied in order to have a continuous extraction and surface-reactivation loops. The optimization of this protocol allowed an analysis of the efficiency of the developed method both in terms of throughput and energy consumption. Microstructural and compositional characterization then was necessary to identify the nature of the obtained compounds, defining the effectiveness of the overall process in terms of material extraction and components separation in order to reduce the required steps to obtain high purity grades of raw materials.File | Dimensione | Formato | |
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2023_05_Bidinotto_01.pdf
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Descrizione: Thesis
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12.28 MB
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2023_05_Bidinotto_02.pdf
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Descrizione: Executive Summary
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3.9 MB
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3.9 MB | Adobe PDF | Visualizza/Apri |
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https://hdl.handle.net/10589/212724