Effect of ammonia molecules on the separation of pentlandite from serpentine using copper (II) as activator

Pentlandite, the material containing more than 90% of the world's nickel, is typical purified by froth flotation followed by mixing the concentrate with relatively high levels of MgO silicates. Furthemiore, serpentine, a source of magnesium silicate, just like pentlandite, can be activated using cupric ion at the pH from 7 to 10, where copper hydroxides are stable species adsorbed on the mineral surface to promote xanthate adsorption. In this study, we used a copper ammonium complex as the selective activator for the pentlandite flotation; it showed a good adaptability to temperature and pH. Compared with the best activation effect of CuSO4, in the actual mineral flotation, the recovery of pentlandite using a cuprammonium solution as an activator increased by 10.18% with a slight decrease in the MgO level, whereas that of pure pentlandite flotation increased by 14%. Compared with the CuSO4 solution, Cu(NH3)(4)(2+) is the main stable species of the copper ammonium solution in mild alkaline solution (pH < 13). This has been confirmed by the UV absorption spectra analysis, thermodynamic analysis, and electrochemical tests. Furthermore, the presence of Cu(NH3)(4)(2+) not only allows for the activator to be a cation and reduces Cu(OH)(2) to avoid activating serpentine, but also reduces the energy required for the redox reaction to form a hydrophobic surface on the mineral-copper-collector; in brief, it increased the flotation and recovery rates. In addition, the density functional theory proved that NH3 can effectively promote the adsorption of copper ions onto the adjacent sulfur atom.