Dumping or disposal of fly ash causes environmental pollution and huge waste
of valuable metals. In this work, carbothermic reduction of fly ash under
normal pressure to produce Al-Si-Fe alloy, and thermal reduction of magnesia
to produce magnesium in vacuum with Al-Si-Fe alloy were investigated. In
addition, the surface morphology and composition of Al-Si-Fe alloy and
magnesium were studied by means of SEM-EDS, XRD. Based on the thermodynamic
analysis, it was found that AlN and SiO2 lowered down the reduction
temperature of SiC and Al4C3, respectively. Increase of temperature and
decrease of vacuum degree promotes the thermal reduction of magnesia.
Results showed that the recovery rate ranked Fe, Si, and Al in a descending
order. The evaporation loss of gaseous SiO and Al2O reduced the recovery of
Si and Al. Al-Si-Fe alloy containing 33.12% Al, 48.73% Si and 6.41% Fe is
obtained under the optimal conditions. Magnesium with content of 94.87% is
prepared using the obtained Al-Si-Fe alloy as reductant. The nucleation rate
is less than the growth rate during the condensation of magnesium vapor.
Thermal process for magnesium production with Al-Si-Fe from coal fly ash: Thermodynamics and experimental investigation