The transformation process of the natural kaolinite into metakaolinite for its use
as a cement addition is very known for long time ago. However, environmental
policies prioritize the waste recycling as raw material by its environmental
benefits. This paper 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 in order 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.