- freely available
Metals 2017, 7(8), 321; https://doi.org/10.3390/met7080321
2. Materials and Methods
2.1. Experimental Materials
2.2. Equipmental and Analytical Method
2.3. Experimental Procedure
3. Results and Discussion
3.1. Thermodynamic Feasibility Analysis
3.2. Influence Factors on the Crystallization of Magnetite
3.2.1. Holding Time
3.2.3. Air Flow Rate
3.3. Magnetic Separation
3.3.1. Particle Size
3.3.2. Magnetic Flux Density
3.3.3. Optimal Conditions
- It can be seen from the thermodynamic analysis that fayalite in nickel slag cannot be decomposed spontaneously, even with temperatures of up to 1873 K, but can be oxidized into magnetite with the help of CaO and O2. Liquidus projection of FeO-SiO2-MgO-CaO-O2 shows that the addition of CaO can not only expand the spinel phase zone, but also obviously decrease the liquidus temperature.
- Fayalite in nickel slags can be oxidized to form magnetite phase in air at high temperature. The holding time, temperature, and air flow rate significantly affect the crystallization behavior of magnetite, while the addition of CaO affects it slightly. The average diameter size of the magnetite reaches 20 μm after undergoing a holding process at 1623 K for 20 min. Temperature and air flow rate obviously affect the shapes of magnetite, which exhibits spherical, polyhedral and skeletal shapes.
- The iron recovery and grade are obviously affected by particle size and magnetic flux density. The iron recovery decreases with the decrease of particle size, while the iron grade reaches a maximal value at 38 μm. As the magnetic flux density increases, the iron recovery initially increases rapidly, reaching a maximal value at 120 mT, while the iron grade remains almost constant.
- The final iron recovery and grade reaches 75.99% and 54.08%, respectively, via multi-step magnetic separation, instead of single magnetic separation. Iron in the concentrate mainly exists in the form of magnetite and magnesium ferrite; and the contents of siderophile elements (Ni, Co) in the final concentrate were also higher than that of the raw slags.
Conflicts of Interest
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