通过对高岭石和铝土矿焙烧过程物相变化的Ｘ射线衍射研究，阐明了铝土矿化学选矿预脱硅的机理。实验表明，矿石中固有的αＳｉＯ２（石英）是不能被脱除的，只有在焙烧温度高达９００℃以上、由偏高岭石分解形成的那部分非晶ＳｉＯ２才能被ＮａＯＨ溶出而脱除。此外，溶出精矿的相分析结果澄清了过去认为在低压溶出脱硅条件下高岭土是稳定存在的误解。给出了提高铝土矿铝硅比值的最佳焙烧工艺制度。 Through the X-ray diffraction study on the phase transformation of kaolinite and bauxite roasting process, the mechanism of pre-desilication of bauxite chemical beneficiation was elucidated. Experiments show that the ores can not be removed from the αSiO2 (quartz). Only when the calcination temperature is above 900 ℃, the part of amorphous SiO2 decomposed by metakaolin can be removed by NaOH dissolution. In addition, the results of phase analysis of the eluted concentrate clarify the misunderstanding that kaolin was stable under the conditions of low-pressure dissolution and desilication. The optimal roasting process system for increasing the ratio of aluminum to silicon in bauxite is given.