关键词: 氢气, 红土镍矿, 硫酸钠, 晶相转变, 磁选分离

Abstract: Hydrogen was experimentally selected as a reducing agent and sodium sulfate as an auxiliary additive. The reduction of the low-grade nickel laterite ore was carried out in a self-made gas-solid reactor with provisions for agitation control by changing the temperature，time，Na2SO4 dosage and H2/N2 volume ratio，and the magnetic separation of the reduced ore was performed using a magnetic separator to prepare high-grade nickel-iron alloy. The mineralogical properties of the raw laterite ore，reduced ore and magnetic concentrate were characterized using thermodynamical calculation，differential thermogravimetry-differential scanning calorimeters (DTG-DSC)，hydrogen-temperature programmed reduction (H2-TPR)，X-ray diffractometry(XRD)，and optical microscopy. The experimental results show that the addition of sodium sulfate could accelerate the crystal phase transition of laterite ore and elevate the utilization of H2. The increase of reduction temperature，as a heat source，could enhance the catalytic reaction activity of sodium sulfate significantly and improve the content of nickel and iron of magnetic product. The optimal reduction condition was obtained as the selective reduction of laterite ore at 800 ℃ for 220 min in the presence of 20% Na2SO4 with an inlet gas mixture of 70% H2 in N2 at a total gas flow rate of 200 L/h. The maximum nickel content and recovery of magnetic product were 6.43% and 97%，respectively. From a thermodynamic point of view，it can be known according to the Gibbs free energy and equilibrium vapor phase diagrams that the sodium sulfate could react with MgSiO3 which exists in the minerals spontaneously at around 700 ℃ and release the nickel. Besides，the generated SO2 could promote FeO transform into FeS，which were conductive to the formation of Fe-S solid solution and thereby contributed to directional mass transfer，accelerated the coalescence of metallic ferronickel particles and facilitated the downstream magnetic separation.

Key words: hydrogen, nickel laterite ore, sodium sulfate, crystalline phase transformation, magnetic separation