Abstract One inconvenience presented by the thermal activation of kaolinite-based wastes is their low content of metakaolinite, a highly pozzolanic product listed in current standards for the manufacture of commercial cements. The addition of a chemical activator during the thermal activation process is a priority line of research to increase the reactivity of the recycled metakaolinite. In this paper, an additional chemical activator, ZnO, is studied and its effect on both pozzolanic properties and the evolution of mineralogical phases in the thermal activation of coal waste with a reaction time of up to 90 days in the pozzolan/lime system. To do so, activation temperatures of between 550 °C/650 °C were selected and additions of chemical activator (ZnO) in percentages of between 0.0% and 3.0% by weight of coal waste, because it is an activator with a positive effect on a 100% natural kaolinite. The results showed that the incorporation of ZnO inhibited the reactivity of the recycled metakaolinite and in consequence, the capacity of the metakaolinite to react with the surrounding lime; even more so when the content of added chemical activator was raised, albeit with some exceptions, in the samples activated at 550 °C and 650 °C with 0.5% of chemical activator. In none of the cases under analysis was the chemical activator able to improve the properties of the metakaolinite in comparison with the properties of the reference sample activated only with temperature. The hydrated phases that appeared in the pozzolanic reaction were tetracalcium aluminate hydrate, stratlingite, monosulfoaluminate hydrate and LDH (phyllosilicate/carbonate).

中文翻译：

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ZnO 对高岭石基废煤活化的影响：火山灰/石灰系统中的火山灰活性和矿物学

摘要 高岭石基废物的热活化带来的一个不便之处是其偏高岭石含量低，偏高岭石是目前商业水泥制造标准中列出的一种高火山灰产品。在热活化过程中添加化学活化剂是提高回收偏高岭石反应性的优先研究方向。在本文中，研究了另一种化学活化剂 ZnO 及其对火山灰性质和在火山灰/石灰体系中反应时间长达 90 天的煤废料热活化过程中矿物相演变的影响。为此，选择了介于 550 °C/650 °C 之间的活化温度，并以煤废料重量的 0.0% 至 3.0% 的百分比添加化学活化剂 (ZnO)，因为它是一种对 100% 天然高岭石具有积极作用的活化剂。结果表明，ZnO的掺入抑制了再生偏高岭石的反应性，从而降低了偏高岭石与周围石灰反应的能力；在 550 °C 和 650 °C 下用 0.5% 的化学活化剂活化的样品中，当添加的化学活化剂的含量增加时更是如此，尽管有一些例外。在所分析的所有情况下，与仅用温度活化的参考样品的性质相比，化学活化剂都不能改善偏高岭石的性质。火山灰反应中出现的水合相是铝酸四钙水合物、水钙石、单硫铝酸盐水合物和 LDH（层状硅酸盐/碳酸盐）。