The transformation process of the natural kaolinite into metakaolinite for its use as a cement addition was very much known long time ago. However, environmental policies prioritize the waste recycling as raw material by its environmental benefits. This article reports, for the first time, the scientific aspects related to the recycling of three Spanish coal mining wastes of different nature and origin, as an alternative source to obtain future pozzolans based on metakaolinite. The effect of activation conditions on the mineralogy, as well as the formation and evolution of hydrated phases formed during the pozzolanic reaction, was analyzed using different instrumental techniques such as X-ray fluorescence, X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and scanning electron microscopy. The results showed that all activated coal mining wastes exhibited high pozzolanic activity. The identification and evolution of hydrated phases with the hydration time in activated kaolin/Ca(OH)2 system were directly related to the origin and nature of the starting coal mining waste and not to the activation temperature itself. Finally, the coal mining wastes are suitable for being used as future pozzolans.
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