Behavior of silicon in vacuum carbothermic reduction of saprolite nickel laterite

The impacts of the addition of pure silica powder the on carbothermic reduction of saprolite nickel laterite in vacuum were studied. The pellets were made of powders of pure SiO 2, Fe 2O 3 and coal. The slag was characterized with X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and conventional chemical analysis. The results show that the molar ratio of Fe/Si and C content significantly affect the volatilization and reduction rate of silica in the carbothermic reduction at a pressure of 2~200 Pa. Moreover, the Gibbs free energies and critical temperatures of the Fe and Si oxides were calculated, based on thermal dynamics. At 100 Pa, the critical temperature of SiO 2 was found to be 477~584 K lower than that at atmosphere. The experimental results show that as the Fe/Si molar ratio and C content increased, the volatilization rate of Si decreased, whereas its reduction rate increased. SiO 2 was found to change into gaseous SiO, most of which turned into Si and SiO 2 after deposition on graphite condenser. And a small amount of gaseous SiO was observed to react with CO, forming solid phased SiC. Some quartz was observed inside the deposits of the compact Fe-Si alloy and SiC in the slag.