Copper activation mechanisms on pyrrhotite Superstructures: Insights from Flotation, synchrotron diffraction and DFT calculations

The use of copper sulfate to enhance pyrrhotite flotation is common in gold processing, yet the activation mechanisms remain unclear due to the coexistence of multiple pyrrhotite superstructures. This study applied advanced mineralogical techniques, including magnetic colloid separation, electron backscatter diffraction (EBSD) and synchrotron X-ray powder diffraction, to identify pyrrhotite phases in two gold ores. It was identified that one ore contained 4C, 5C and 6C pyrrhotite superstructures, while the other included only 5C and 6C superstructures. In both ores, 6C was dominant, followed by 5C, with minor 4C. Flotation tests coupled with mineralogical analysis showed that 5C pyrrhotite achieved the highest CuSO 4 -activated recovery, followed by 6C and 4C. To explain this trend, density functional theory (DFT) calculations were performed. Cu 2+ adsorption was strongest on 5C and 6C surfaces via Cu–S bonding and significant charge transfer, enhancing surface reactivity. Additionally, the 5C structure exhibited greater electronic delocalization in Fe orbitals, promoting more stable Cu adsorption and stronger activation under neutral pH. In contrast, Cu(OH) 2 preferentially adsorbed on 4C surfaces via Fe–O bonds, forming passivating layers that suppressed flotation. These results demonstrated that the superior floatability of 5C pyrrhotite arose from its favorable surface electronic structure and higher affinity for Cu 2+ , which promoted effective collector attachment and enhanced hydrophobicity. These findings established a clear link between pyrrhotite crystal structure, copper speciation and surface chemistry, offering new insights into how specific activation pathways govern flotation performance.