Sulfidation of Ternary Oxides: A Thermodynamic and Experimental Study Toward Selective Metal Extraction

Abstract

Conventional metal refining techniques face growing challenges due to increasing ore complexity and their limited ability to accommodate post-consumer recycling feedstocks. Sulfidation is a promising pyrometallurgical approach for the selective separation and recovery of critical elements from such complex feedstocks. This thesis presents a chemical thermodynamic framework for the sulfidation of divalent alkaline earth and transition metal ternary oxides of titanates, molybdates, tungstates, niobates, and tantalates. Modified predominance diagrams were constructed to determine the possible sulfidation outcomes, and a sensitivity analysis on the input thermodynamic data was performed to assess their impact on the outcome of sulfidation. A high-temperature apparatus was designed and tested to compare predicted and observed sulfidation behavior. Together, the model and experimental apparatus provide a new experimental method to estimate the high-temperature Gibbs energy of multicomponent oxides. Application to current chemical metallurgy challenges, including the recycling of tantalum-based capacitors and the refining of tungsten-bearing ores, underscore sulfidation as a powerful step to support new processing route for sustainable metal recovery.