Study of the Thermal Stability of Faujasite Zeolite Synthesized from Kaolin Waste from the Amazon

The waste from the processing of kaolin in the Amazonian region of Brazil was subjected to a calcination process at 700°C for 2 h to obtain metakaolin, which, together with sodium hydroxide and sodium silicate, formed the reaction mixture. This mixture was subjected to an aging step (24 h at 60 rpm), and a subsequent hydrothermal process at 110°C for 10 h. By means of X-ray diffraction (XRD), differential thermal and thermogravimetric analysis (DTA/TG) and scanning electron microscopy (SEM) techniques, the crystallization of a single phase, faujasite (FAU) zeolite, was observed. In the postsynthesis process, it was verified by means of XRD that the thermal stability of this structure persists up to a temperature of 600°C. At 800°C, the structure of FAU collapses. Beginning at 850°C, new nepheline phases are formed, and at 1000°C, nepheline and mullite phases are formed.

以巴西亚马逊地区高岭土加工产生的废弃物为原料，经700℃煅烧2小时制得偏高岭石（metakaolin）；将其与氢氧化钠、硅酸钠混合制备得到反应混合物。该混合物先经60 rpm转速下陈化24小时的步骤，随后在110℃下进行10小时的水热反应。通过X射线衍射（X-ray diffraction, XRD）、差热-热重分析（differential thermal and thermogravimetric analysis, DTA/TG）以及扫描电子显微镜（scanning electron microscopy, SEM）等表征手段，可观察到单一物相——八面沸石（FAU，faujasite）分子筛的结晶生成。在后合成过程中，经XRD验证，该FAU结构的热稳定性可维持至600℃；当温度升至800℃时，FAU结构发生坍塌。当温度达到850℃时，体系开始生成新的霞石（nepheline）物相；在1000℃时，体系中同时生成霞石与莫来石（mullite）物相。