Recovering Magnesium from Ferronickel Slag by Vacuum Reduction: Thermodynamic Analysis and Experimental Verification

Abstract

The feasibility of recovering magnesium from ferronickel slag by vacuum reduction was evaluated. The thermodynamic calculations indicated that the magnesia in slag can be reduced to gaseous magnesium by Si, FeSi, Al, and C, with the minimum reduction temperatures of 2324, 2530, 1678, and 2580 K at 100 000 Pa, respectively. As the system pressure decreases, the minimum reduction temperatures decline significantly. Si maintains the minimum reduction temperature of 1585–1673 K at the atmospheric pressure of 10–100 Pa, acting as a suitable reducing agent for recovering magnesium. To verify the findings, preliminary vacuum reduction experiments, in which CaO was added to eliminate the adverse impact of SiO2 in slag, were carried out. By reducing slag with additions of 50 wt % Si and 30 wt % CaO at 1573 K for 3 h at 10 Pa, the recovery of magnesium reached 97.74%.

Reverse leaching of magnesium from ferronickel slag using alkali solvent NaOH

“…Gaseous magnesium resulted from the process since it is the lightest metal present in the raw materials. 97.74 % Mg resulted from the condensation of the gaseous metal [27]. However, this process needs high energy consumption since the condition process is performed at high temperatures and vacuum.…”

Decomposition of ferronickel slag through alkali fusion in the roasting process

“…These are disodium magnesium silicate [4,7] and sodium chromate [4], which were observed from the roasting process that used sodium compound such as Na 2 O 2 [4] and NaOH [7] as an additive in the roasting process at about 500-600 °C for 1 hour. Moreover, selective extraction of elemental chromium from ferronickel slag via microwave roasting with sodium peroxide addition followed by water leaching yielded 94.21 % soluble chromium, while only 0.06 % by weight of chromium remained in the leach residue [21]. Sodium chromate formation is beneficial since it can be separated by water leaching and prevent environmental pollution.…”

An Overview of Precious Metal Recovery from Steel Industry Slag: Recovery Strategy and Utilization

“…When the coal-to-slag ratio was maintained at 0.05, these quantities in the metal phase decreased (12% for copper and 20% for cobalt), but recoveries improved to 65% and 90%, depending on the reduction period. The research also revealed that higher temperatures improve reaction kinetics, whereas lower temperatures result in greater quality metal output . In a similar study, Maweja et al also manifested that under 1400 °C temperature carbothermic reduction could exhibit higher metal recovery.…”