Bidentate Chelation-Driven Selective Depression of Pyrite: Adsorption Mechanism and Flotation Application of an N-Heterocyclic Carboxylic Acid Depressant

The selective flotation separation of chalcopyrite and pyrite constitutes a core bottleneck in the comprehensive utilization of copper–sulfur ores. Given the proneness of pyrite to copper activation and pipeline scaling defects induced by the conventional high-alkaline lime depression process, novel organic depressants with outstanding selectivity under weak alkaline media are urgently required to be developed. In this study, 3-hydroxy-2-pyridine carboxylic acid (3-HPA) was adopted as a novel eco-friendly organic depressant to realize the selective flotation separation of chalcopyrite from pyrite under weakly acidic conditions (pH = 6). The selective depression mechanism of 3-HPA against pyrite was systematically investigated via microflotation assays, multiscale surface characterizations, and first-principles theoretical computations. Flotation experimental data verified that 3-HPA is capable of selectively depressing pyrite floatability while maintaining excellent floatability of chalcopyrite, with a maximum recovery gap of 92.71% observed between the two minerals. Collectively, 3-HPA serves as an efficient and highly selective organic depressant for pyrite. On pyrite surfaces, 3-HPA undergoes bidentate chelation with surface iron active sites: the nitrogen atom on its pyridine ring and the oxygen atoms of the carboxyl group coordinate with Fe atoms to generate stable Fe–N and Fe–O bonds, which drastically reduce the surface hydrophobicity of pyrite. By comparison, only feeble intermolecular interactions take place between 3-HPA and chalcopyrite surfaces, whereby the surface hydrophobicity of chalcopyrite remains intact. The present research clarifies the selective depression mechanism of 3-HPA against pyrite and provides new theoretical guidance for the development of green and efficient pyrite depressants.