Termination-dependent surface chemistry of pyrochlore flotation: stability, hydration, and collector adsorption

• First study to reveal twin surface reactivity from mineral breakage. • Oxygen-terminated pyrochlore surfaces dominate under flotation conditions. • Hydrophilic pyrochlore surfaces exhibit strong collector adsorption. • Protonated amines show powerful affinity for hydroxylated pyrochlore surfaces. • Collector adsorption involves H bonding beyond Nb–N coordination. Pyrochlore, the primary mineral in niobium-bearing ores, generates diverse surface terminations during comminution, which can influence subsequent froth flotation. Using density functional theory (DFT) simulations, we evaluated the stability of all possible low-index pyrochlore surface terminations and analyzed their interactions with water and amine collectors. The simulations revealed that oxygen-terminated surfaces are more stable than metal-exposed ones. We also examined hydration behavior, which precedes collector interaction during flotation. Oxygen-terminated surfaces readily undergo hydroxylation, forming strong covalent bonds and dense hydration layers, while metal-terminated surfaces exhibit weaker hydrogen bonding and greater hydrophobicity. To simulate pH-dependent flotation conditions, we investigated the adsorption of neutral and protonated amines on hydroxylated (hydrophilic) and bare (hydrophobic) surfaces. Importantly, this study is the first to explicitly consider twin surfaces—the metastable counterparts of thermodynamically favored planes that are generated by mechanical breakage—and to reveal their distinct surface terminations and reactivity. Contrary to the prevailing assumption that Nb–N bonding dominates, our results revealed multiple adsorption mechanisms. Notably, hydrophilic surfaces exhibited enhanced adsorption, especially in the presence of protonated collectors. These results emphasize the importance of considering termination-specific adsorption pathways and collector speciation when designing effective pyrochlore reagents. Elucidating these surface-dependent interactions provides new insights for the development of selective reagents.