Abstract
The iron resources in nickel slag were recycled by oxidation and magnetic separation. The effects of holding time, temperature, air flow rate and basicity on the crystallization of magnetite were investigated systematically. Moreover, the influence of particle size and magnetic flux density on the recovery and grade of iron during the magnetic separation was also explored. Results showed that the magnetite particles were significantly influenced by holding time, and the average diameter size reached about 20 μm after holding for 20 min at 1623 K. The holding temperature obviously affected the microstructure of magnetite phases: with the increase in holding temperature, the shapes of the magnetite particles changed from polyhedral form to skeletal particles. As the air flow rate was increased to 170 mL/min, the magnetite developed into tiny spherical particles due to the strong stirring. It was also found that the crystallization of magnetite was slightly effected by basicity. The iron recovery reduced with the decrease of particle size, while the iron grade first increased to a maximal value of 38 μm, and then decreased. As the magnetic flux density increased, the iron recovery initially increased rapidly, reaching a maximal value at 120 mT, while the iron grade remained almost constant. The final iron recovery and grade were 75.99% and 54.08%, respectively, via multi-step magnetic separation instead of single magnetic separation. Iron in concentrate mainly exists in the form of magnetite and magnesium ferrite, and contents of siderophile elements (Ni, Co) in final concentrate were also higher than that of raw slags.
Highlights
Due to the high content of iron and value-added metals, such as Ni, Co, Cu, iron-rich nickel slag can be considered to be an important secondary source of metals, especially for iron ore
Semykina [5] presented the kinetics of the oxidation of divalent
Semykina [5] presented the kinetics of the oxidation of divalent iron to a trivalent state in liquid FeO-Calcium oxide oxide (CaO)-SiO2 slags
Summary
Due to the high content of iron (about 36–45 wt % [1]) and value-added metals, such as Ni, Co, Cu, iron-rich nickel slag can be considered to be an important secondary source of metals, especially for iron ore. The only way to recover iron from nickel slag efficiently is by reduction-magnetic separation [2,3,4]. In this process, coke or coal is used to reduce fayalite (Fe2 SiO4 ) in nickel slag, while producing iron and silicates; CaO is added to improve the reaction rate by destroying the structure of the silicates. Several disadvantages of this method have limited its industrial applications:. An environmentally friendly method for iron recycling from slags by an oxidation process has prompted wide attention. Numerous scholars have studied the oxidation of the iron-bearing phase in slag systems. Semykina [5] presented the kinetics of the oxidation of divalent
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