红土镍矿真空碳热还原过程中硅的挥发行为

Behavior of Silicon in Vacuum Carbothermic Reduction of Saprolite Nickel Laterite

为了解红土镍矿在真空碳热还原过程中SiO2的还原特性和还原过程的主要影响因素,在系统压力2～200 Pa下,以分析纯的SiO2、Fe2O3以及煤炭为原料,在热力学分析的基础上,采用X射线衍射、扫描电子显微镜-能量散射谱和化学成分分析等手段,研究了Fe/Si摩尔比、配碳量对SiO2还原过程、硅的挥发率和还原反应速率的影响。通过热力学计算,得出Fe,Si氧化物被碳还原的化学反应自由能和还原反应临界温度,表明在100 Pa条件下SiO2的临界反应温度降低了477～584 K。实验结果表明:Fe/Si摩尔比的增大和配碳量的增加,均降低了Si的挥发率,提高了SiO2还原反应速率;SiO2发生了气化反应生成了SiO气体并在石墨冷凝系统歧化生成Si和SiO2,且有部分SiO气体与石墨或者CO反应生成SiC;反应残渣中的石英颗粒被Fe-Si合金和SiC包围,结合紧密。

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 SiO2, Fe203 and coal. The slag was characterized with X-ray diffraction, scanning electron rniemscopy, 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 SiO2 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 in- creased, the volatilization rate of Si decreased, whereas its reduction rate increased. SiO2 was found to change into gaseous SiO, most of which turned into Si and SiO2 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.