This doctoral thesis addresses the accelerating deployment of renewable energy technologies, which has intensified demand for critical and precious materials while simultaneously generating rapidly growing electronic waste streams. End-of-life crystalline silicon photovoltaic modules and spent lithium-ion batteries are particularly important in this context because they contain economically valuable and strategically significant elements, including silver and lithium. However, their recovery remains constrained by technical complexity, reagent consumption, process selectivity, and scalability. Accordingly, this thesis investigates sustainable hydrometallurgical and electrochemical strategies for recovering silver and lithium from these emerging secondary resources, with emphasis on process optimization, selectivity, material purity, and circular-economy relevance. The initial phase of the study was focused on the recovery of silver from silicon solar cell waste, in which a base-activated persulfate-ammonium leaching system was optimized using a design of experiments. This system suppressed copper co-dissolution by forming a passivating copper (II) oxide layer, thereby resolving interference caused by the similar reduction potentials of silver and copper. Following that, silver was recovered by electrodeposition redox replacement reaction using copper as the sacrificial metal, yielding 98.7 ± 1.4% pure silver. In the subsequent phase of the research developed a direct electrochemical route for the recovery of lithium from spent LiFePO4 batteries. In a two-electrode cell with Na2 SO4 electrolyte, anodic oxidation of LiFePO4 to FePO4 released lithium into solution, which was subsequently precipitated as Li3 PO4 . The electrocatalytic leaching conditions were optimized by a face-centred central composite design, yielding a lithium leaching efficiency of ~92% and a selectivity of ~96%, while transition-metal concentrations remained essentially unchanged. The recovered Li3 PO4 reached 89% precipitation efficiency and 99% purity, avoiding the multiple separation steps required by conventional hydrometallurgy. The third phase of study was directed towards the introduction of a fully bio-based leaching stage for lithium recovery from LiNixCoyMnzO2 black mass, using Arbutus unedo L. distillers’ grains as both a reducing agent and a leaching medium. This “waste treats waste” approach eliminated mineral acids and synthetic reductant. Under conditions optimized by a central composite circumscribed design, lithium recovery reached 85 ± 1.3% with ~88% selectivity, while Ni and Co co-leaching remained below 4%. Polyphenols, reducing sugars, and organic acids in the extract supported reductive dissolution and metal complexation. Sequential precipitation then recovered manganese and lithium at above 90%, as Mn(OH)2 and high-purity Li2 CO3 (99.76%). Based on the foregoing findings, this thesis demonstrates that chemometrically optimized electrochemical and biomass-assisted hydrometallurgical processes can provide selective, efficient, and lower-impact routes for recovering valuable materials from electronic waste. These findings contribute to the development of circular strategies for critical materials recovery, reduce dependence on primary resources, and provide a foundation for future scale-up supported by lifecycle and techno-economic assessment.
RECOVERY OF CRITICAL MATERIALS FROM ELECTRONIC WASTE
AWAIS, MUHAMMAD
2026-09-18
Abstract
This doctoral thesis addresses the accelerating deployment of renewable energy technologies, which has intensified demand for critical and precious materials while simultaneously generating rapidly growing electronic waste streams. End-of-life crystalline silicon photovoltaic modules and spent lithium-ion batteries are particularly important in this context because they contain economically valuable and strategically significant elements, including silver and lithium. However, their recovery remains constrained by technical complexity, reagent consumption, process selectivity, and scalability. Accordingly, this thesis investigates sustainable hydrometallurgical and electrochemical strategies for recovering silver and lithium from these emerging secondary resources, with emphasis on process optimization, selectivity, material purity, and circular-economy relevance. The initial phase of the study was focused on the recovery of silver from silicon solar cell waste, in which a base-activated persulfate-ammonium leaching system was optimized using a design of experiments. This system suppressed copper co-dissolution by forming a passivating copper (II) oxide layer, thereby resolving interference caused by the similar reduction potentials of silver and copper. Following that, silver was recovered by electrodeposition redox replacement reaction using copper as the sacrificial metal, yielding 98.7 ± 1.4% pure silver. In the subsequent phase of the research developed a direct electrochemical route for the recovery of lithium from spent LiFePO4 batteries. In a two-electrode cell with Na2 SO4 electrolyte, anodic oxidation of LiFePO4 to FePO4 released lithium into solution, which was subsequently precipitated as Li3 PO4 . The electrocatalytic leaching conditions were optimized by a face-centred central composite design, yielding a lithium leaching efficiency of ~92% and a selectivity of ~96%, while transition-metal concentrations remained essentially unchanged. The recovered Li3 PO4 reached 89% precipitation efficiency and 99% purity, avoiding the multiple separation steps required by conventional hydrometallurgy. The third phase of study was directed towards the introduction of a fully bio-based leaching stage for lithium recovery from LiNixCoyMnzO2 black mass, using Arbutus unedo L. distillers’ grains as both a reducing agent and a leaching medium. This “waste treats waste” approach eliminated mineral acids and synthetic reductant. Under conditions optimized by a central composite circumscribed design, lithium recovery reached 85 ± 1.3% with ~88% selectivity, while Ni and Co co-leaching remained below 4%. Polyphenols, reducing sugars, and organic acids in the extract supported reductive dissolution and metal complexation. Sequential precipitation then recovered manganese and lithium at above 90%, as Mn(OH)2 and high-purity Li2 CO3 (99.76%). Based on the foregoing findings, this thesis demonstrates that chemometrically optimized electrochemical and biomass-assisted hydrometallurgical processes can provide selective, efficient, and lower-impact routes for recovering valuable materials from electronic waste. These findings contribute to the development of circular strategies for critical materials recovery, reduce dependence on primary resources, and provide a foundation for future scale-up supported by lifecycle and techno-economic assessment.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
