Thermal process for magnesium production with Al-Si-Fe from coal fly ash: Thermodynamics and experimental investigation

Abstract

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.

A novel method for alumina preparation by electrotransformation AlCl3 solution under NH4Cl-catalyzed and CO2-injected conditions

“…Although quite a bit of fly ash is widely used for low-value applications in the production of bricks, cement, concrete, ceramic products, building materials, and road bases [2][3][4][5][6][7], a large portion of fly ash is still discharged arbitrarily into the environment. The discharge of this industrial waste not only occupies a large amount of potential agricultural land [8] and endangers human health, but it also brings a serious of environmental burden, causing local river congestion, water pollution, PM2.5 rise, and other problems [9][10][11]. The annual emission of fly ash in the world is as high as 500 million tons [12], with the annual emission of fly ash in China as high as 50 million tons [13], which is approximately 10% of the world fly ash annual emission.…”