A great deal of nickel slag containing a lot of Fe in the form of FeO is produced in the process of nickel smelting. The effect of FeO content on the melting characteristics and structure of nickel slag is studied via thermodynamic calculation and experiments, with the nickel slag of water quenching furnace as raw material, which is simplified to CaO-SiO2-FeO-MgO slag system. The results are shown as follows: with the increasing of FeO content, the precipitated primary phase changes from melilite to olivine. The liquidus temperature, softening temperature, hemispheric temperature, flow temperature, viscosity and critical viscosity temperature of slag system tends to decrease gradually, but the solid phase temperature tends to decrease first and then increase. The centre of [SiO4]4- tetrahedron symmetric stretching vibration band in the slag system moves to the low wave number region. The mole fraction of O0 in the slag decreases continuously, the mole fraction of O- and O2- increases. The complex silicon-oxygen tetrahedron structure gradually disintegrates and the structural unit tends to be simple.

Nickel slag is a kind of solid waste with a high yield and low utilization rate.However, there is a large amount of Fe in nickel slag, which mainly exists in the form of fayalite.In this study, nickel slag is used as raw material. The addition of CaO can destroy the network structure of fayalite, and the iron-rich phase can be oxidized to magnetite under oxidation condition. It is beneficial to the recovery of iron resources. The effect of basicity on structural reconstruction of molten slag and precipitation of magnetite is investigated. The results show that when the basicity is 0.38~1.50, the degree of polymerization of silicate structure decreases with the increase of basicity. When the temperature is 1450~1500℃, viscosity of slag decreases first and then increases with the increase of basicity. The viscosity is the lowest with the basicity of 0.90, and the granular magnetite begins to precipitate during the non-equilibrium solidification at 1455℃. The growth rate of the magnetite is 1.20 μm/s at 0~10 s, which is significantly higher than the magnetite growth rate of 0.16 μm/s at 10~22 s, and the grain size of the magnetite remains unchanged after 22 s.