The present study aimed to optimize the calcination process parameters (viz., temperature, time, and particles size) for the extraction of aluminum from Ethiopian kaolinite. The kaolinite calcination was done in the temperature of 600–700°C, time of 120–180 min, and particles size of 106–355 μm. The extraction of aluminum from calcined kaolinite was carried out at fixed acid concentration of 3 M, temperature of 80°C, liquid-to-solid ratio of 12 mL g⁻¹, time of 120 min, and stirring speed of 700 rpm. The chemical composition of kaolinite was determined using XRF. Moreover, kaolinite, metakaolinite, and extracted aluminum were characterized by XRD, TGA, DSC, and FTIR. The XRF result of the kaolinite was mainly silicon oxide (55.76% w/w), aluminum oxide (32.02% w/w), and loss on ignition (11.17% w/w). Calcination of kaolinite produced amorphous metakaolinite due to the dehydroxylation reaction as shown by the FTIR results. Three endothermic peaks and one exothermic peak were detected in the thermal analysis of the kaolinite due to water removal, impurities decomposition, dehydroxylation reaction, and phase change from metakaolinite to spinel, respectively. The extracted aluminum proportionally increased with kaolinite calcination temperature and time. However, the extracted aluminum increased as the particles size reduced. The extracted aluminum was in the form of aluminum chloride hexahydrate and trigonal crystalline structure. The optimum values of the degree of conversion of kaolinite dehydroxylation reaction and extracted aluminum of 0.992 and 71.28% w/w were obtained at the optimum kaolinite calcination temperature of 700°C, time of 180 min, and particles size of 106 μm, respectively.

中文翻译：

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埃塞俄比亚高岭石提铝煅烧工艺参数表征与优化

本研究旨在优化从埃塞俄比亚高岭石中提取铝的煅烧工艺参数（即温度、时间和粒度）。高岭石煅烧温度为 600~700 ℃，时间为 120~180 min，粒度为 106~355  μm。从煅烧高岭石中提取铝是在固定酸浓度 3 M、温度 80°C、液固比 12 mL g ^{-1的条件下进行的。}, 时间 120 min, 搅拌速度 700 rpm。使用 XRF 测定高岭石的化学成分。此外，通过 XRD、TGA、DSC 和 FTIR 对高岭石、偏高岭石和提取铝进行了表征。高岭石的 XRF 结果主要是氧化硅 (55.76% w/w)、氧化铝 (32.02% w/w) 和烧失量 (11.17% w/w)。如 FTIR 结果所示，由于脱羟基反应，高岭石的煅烧产生了无定形偏高岭石。在高岭石的热分析中，由于去水、杂质分解、脱羟基反应和偏高岭石到尖晶石的相变，分别检测到三个吸热峰和一个放热峰。提取的铝随高岭石煅烧温度和时间成比例增加。然而，提取的铝随着颗粒尺寸的减小而增加。提取的铝呈六水合氯化铝和三方晶体结构的形式。在高岭石的最佳煅烧温度为700℃、时间为180分钟、粒径为106 微米，分别。