2026 Theses Doctoral

Electrochemical and First-Principles Approaches to Understanding and Processing Nickel Sulfide Ore Bodies

Donovan, Brian Christopher

Nickel is essential for stainless steel, battery materials, and low-carbon energy infrastructure, but conventional processing of nickel sulfide ore bodies remains energy-intensive and environmentally challenging. Sulfidic nickel concentrates are commonly processed through pyrometallurgical smelting, which requires high temperatures and generates sulfur dioxide emissions, while pyrrhotite-rich wastes and residues can contribute to long-term acid mine drainage. Developing cleaner approaches for nickel sulfide utilization, therefore, requires both practical alternatives to conventional processing and a deeper understanding of the sulfide minerals that control extraction behavior, environmental stability, and reaction energetics.

This dissertation combines electrochemical leaching, process modeling, technoeconomic analysis, and first-principles calculations to study nickel sulfide ore bodies across experimental, process, and atomistic scales. First, the selective removal of pyrrhotite from pentlandite-bearing feedstocks was investigated using ambient-temperature reductive leaching with vanadium(II) and chromium(II). Mineralogical and chemical changes were characterized using automated mineralogy, X-ray diffraction, digestion, and inductively coupled plasma optical emission spectroscopy. Second, the plant-scale feasibility of cerium-mediated oxidative leaching of pentlandite was evaluated using SysCAD flowsheet modeling and technoeconomic analysis, with particular attention to reagent consumption, cerium regeneration, impurity removal, mixed hydroxide precipitate production, and recycle streams. Third, density functional theory was used to develop and validate an r²SCAN+rVV10+U framework for 3d transition-metal sulfides, enabling improved prediction of formation enthalpies, phase diagrams, and aqueous stability. This computational framework was then applied to iron sulfides and pentlandite to determine how magnetic ordering, vibrational free energies, configurational entropy, pressure, and iron- nickel site disorder affect sulfide phase stability.

The experimental leaching studies show that pyrrhotite can be removed rapidly and selectively from pentlandite-bearing solids under ambient conditions, with near-complete pyrrhotite dissolution within minutes and minimal nickel loss. This produces nickel-enriched solid residues and suggests a route for upgrading sulfide concentrates or treating pyrrhotite-rich tailings while reducing the potential for acid mine drainage. The process modeling results show that cerium-mediated oxidative leaching can be integrated into a continuous hydrometallurgical flowsheet, but that reagent consumption, especially base demand, is a major economic constraint. Replacing double-salt precipitation with solvent extraction substantially reduces sodium hydroxide consumption, while bipolar membrane electrodialysis may further improve circularity if membrane fouling and sulfate management can be controlled.

The first-principles studies show that r²SCAN+U substantially improves the thermochemical description of transition-metal sulfides relative to uncorrected r²SCAN, supporting its use for sulfide phase stability calculations. For the iron-sulfide system, zero- Kelvin calculations alone do not explain the prevalence of pyrrhotite in natural ore bodies. However, the inclusion of magnetic, vibrational, and configurational free-energy contributions stabilizes pyrrhotite relative to troilite under more realistic conditions. For pentlandite, machine- learning-guided density functional theory provides a practical route for searching the large configurational space created by iron and nickel disorder on the metal sublattice. The current workflow identifies lower-energy pentlandite configurations and shows that finite-temperature contributions are needed to reconcile calculated stability with experimental observations.

Overall, this dissertation establishes an integrated framework for understanding and processing nickel sulfide ore bodies. The results demonstrate that selective redox chemistry can alter sulfide mineralogy to improve concentrate quality and reduce environmental risk, while process modeling identifies the economic constraints that must be overcome for industrial implementation. At the same time, first-principles calculations clarify the thermodynamic factors that govern pyrrhotite and pentlandite stability. Together, these approaches provide practical and fundamental insight into cleaner strategies for nickel sulfide extraction, residue management, and future hydrometallurgical process design.