Separation and recovery of iron and nickel from low-grade laterite nickel ore by microwave carbothermic reduction roasting

Abstract

An effective strategy to achieve separation and recovery of iron and nickel from low-grade laterite ore via microwave carbothermic reduction roasting is reported. In this work, we determined the underlying reason for the poor separation of iron and nickel during the magnetic separation process. The effect of operating variables on the recovery and separation of nickel and iron from low-grade laterite ore was initially investigated during microwave carbothermic reduction roasting to reveal the underlying reason for their poor separation. Then, the phase transformation and interfacial reduction of fayalite Fe2SiO4 and hortonolite Fe2−xMgxSiO4 in the mineral composition of laterite were systemically investigated via SEM/EDS and XRD analysis to determine the influence of CaO and MgO on the stepwise reduction behavior of Fe2SiO4. Phase transformation during the microwave carbothermic reduction roasting process by microwave irradiation heating occurred according to the following steps: (Fe,Ni)2SiO4 (x = 0) and Mgx(Fe,Ni)2−xSiO4 (0 ≤ x ≤ 2) → MgxCay(Fe,Ni)2−x−ySiO4 (0 ≤ x + y ≤ 2) → MgxCa2−xSiO4. Finally, the substituted iron and nickel ions were found to reduce to ferronickel alloy under a reductive atmosphere. The ferronickel alloy with a nickel grade of 7.05 wt.% and an iron grade of 71.70 wt.% was produced successfully from low-grade laterite ores in which the recovery ratios of nickel and iron were 92.44% and 91.17%, respectively. Furthermore, these methods could be extended to the reduction behavior and interfacial reaction of silicates in other ores.

Keywords

• Laterite ores
• Microwave irradiation heating
• Carbothermic reduction
• Fayalite
• Phase transformation
• Morphologies