Chemical and mineral transformations that occur in mine waste and washery rejects during pre-utilization calcination

• Two types of CMW from the province of León (Spain) were texted to select the most suitable waste in cement industry.
• Mineralogical and chemical composition shows phyllosilicates, quartz, calcite and feldspars.
• The fixed lime results showed that the ACMW product obtained at 900ºC/2 hours presented low activity
• C-S-H gels are hydrated phases during the pozzolanic reaction in ACMW/Ca(OH)2 systems.
• Is possible the scientific viability of CMW as an addition for the manufacture of eco-efficient cement.

The mineralogical content of coal mine waste consists primarily of inorganic compounds which can be converted into a metakaolin-based product under controlled activation conditions that is also a highly pozzolanic material. Activation temperatures ranging from 500 to 900 °C over 2 h retention time affect the mineralogy of coal mine waste, as well as the formation and evolution of the hydrated phases that form during the pozzolanic reaction. The hydrated phases formed during the pozzolanic reaction in the activated coal mine waste (ACMW)/Ca(OH)2 system were C–S–H gels, stratlingite, tetracalcium aluminate hydrate, LDH compounds (phyllosilicate/carbonate) and monosulfoaluminate. Low temperatures (600 °C) favored the formation of LDH compounds and stratlingite; whereas monosulfoaluminate formed during the hydrated phase at higher temperatures (900 °C) during the first day of the pozzolanic reaction, and tetracalcium aluminate hydrate appeared as the dominant crystalline phase at 7 and 28 days.