Structure and Adsorption at the Bastnäsite-Water Interface: Fundamental Investigations toward Rare Earth Mineral Recovery

This dissertation investigates the interfacial structure and reactivity of a rare earth mineral in the context of froth flotation. Bastnäsite [(Ce,La,Nd)FCO3], one of the primary mineral sources of rare earth elements, has been chosen for this investigation. Flotation separation relies on selective adsorption of collector ligands to the desired mineral surface in solution; fundamental understanding of these adsorption reactions will aid in the development of more effective separation technologies.

Chapter 1 presents an introduction to the significance of rare earth minerals and the process of froth flotation. Chapters 2 and 3 address the adsorption reactions of ligand molecules at the interface. Chapter 2 analyzes the adsorption mechanism of octanohydroxamic acid, a popular candidate for bastnäsite flotation. In-situ FTIR reveals mechanistic information that demystifies the quantitative results of the adsorption isotherm. Chapter 3 compares several flotation ligands to determine the effect of ligand structure on the mechanism of adsorption.

In Chapter 4, the structure of the bastnäsite (001) surface is investigated under varying conditions using X-Ray reflectivity. The surface termination is significant because it determines which sites are available for ligand adsorption in the flotation system. Changes in the surface structure are evaluated by fitting a model to a set of crystal truncation rods measured at this interface. This work provides fundamental information about the aqueous geochemistry of bastnäsite flotation on both sides of the interface.