Thermal Concentration of Nickeliferous Pyrrhotite Concentrate for Nickel Recovery Using Metallic Iron: Thermodynamic Assessments and Effects of Process Variables

Direct disposal of nickeliferous pyrrhotite (Pyrr) tailings can cause the formation of acidic effluents and result in significant loss of nickel values. The investigation studies a thermal concentration process for the Pyrr which recovers its nickel content as ferronickel alloy by adding metallic iron. Thermodynamic assessments of the system were conducted to narrow the range of iron addition and treatment temperature for the thermal concentration process. Experimentally, nickeliferous Pyrr concentrate was blended with varying amounts of metallic iron, pressed into briquettes, and then heated at 850–950°C for different lengths of time (10–240 min) in flowing argon. Under these conditions, nickel precipitated out of the sulfide as ferronickel alloy particles, which were magnetically separated. The effects of varying process variables including iron addition rate, treatment time, and temperature on the Ni$$\mathrm{Ni}$$ grade and recovery in the magnetic product are discussed.