Precipitation Behavior of Magnetite Phase during Modified Nickel Slag Treated by Molten Oxidation

Abstract

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°C, 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°C. 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.