Development and Characterization of Electrochemical-Mediated Hydrometallurgic al Processes for Nickel and Copper Extraction
Tongwei Xu, Chemical Engineering
Abstract: The growing demand for critical minerals such as nickel and copper, driven by electrification and the energy transition, is placing increasing pressure on conventional extraction technologies. Current processing routes for sulfide minerals rely heavily on energy-intensive smelting with significant environmental impacts. This dissertation investigates electrochemical-mediated hydrometallurgical processing as a sustainable alternative for extracting nickel and copper from sulfide and unconventional mineral resources using regenerable redox-mediating reagents.
Electrochemically regenerated vanadium(II) and cerium(IV) were employed as reductive and oxidative leaching agents, respectively. Metal extraction, reaction products, and mineral transformations were characterized using ICP-OES, XRD, SEM-EDS, XPS, and XAS to elucidate reaction mechanisms and mineralogical controls on extraction behavior.
For copper extraction, vanadium(II)-mediated leaching selectively dissolved iron from chalcopyrite (CuFeS₂), converting the mineral into copper-rich sulfide phases through a dissolution–precipitation mechanism. Under appropriate conditions, metallic copper could be produced directly during leaching.
For nickel extraction, cerium(IV)-mediated leaching rapidly dissolved pentlandite under ambient conditions, producing elemental sulfur as the primary solid product. Cerium was regenerated electrochemically, and dissolved nickel was recovered as a mixed hydroxide precipitate. Mechanistic studies revealed sulfur-rich surface layers and oxidized nickel and iron intermediates, which enabled the development of a two-step process that further improved nickel recovery. The approach was also successfully applied to unconventional nickel resources, including high-magnesium sulfide concentrates and awaruite-bearing ultramafic materials, demonstrating rapid and selective nickel extraction from feedstocks that are difficult to process by conventional smelting.
Overall, this work demonstrates that electrochemically regenerated redox mediators provide an effective low-temperature platform for extracting critical minerals from diverse feedstocks while advancing the fundamental understanding of sulfide mineral dissolution and phase transformation. These findings support the development of cleaner and more sustainable technologies for critical mineral production.
