Improvement on pozzolanic reactivity of coal gangue by integrated thermal and chemical activation

In order to effectively utilize coal gangue and its calorific value (4180-12,540 kJ/kg), coal gangue was converted into energy-saved cement by activating at 800 °C with an integrated thermal and chemical activation method. Microanalysis with XRD and NMR indicates that improved pozzolanic reactivity for coal gangue contributes to the mineral phase change with amorphous status during thermal and chemical activation process. In the chemical activation process, amorphous materials composed of Q3(0Al), Q3(1Al) and Q0 units were formed from parts of aluminosilicate minerals (quartz and K-feldspar). With the physical and mechanical testing, it shows that CaSO4 + CaO is the most effective additive during the chemical activation, which is a non-equilibrium reaction between coal gangue and CaSO4 + CaO during calcination process. A prototype plant in cement industry also proofs these results. Eco-cement containing 56% of activated coal gangue had been successfully produced for road pavement application with a 28-days concrete compressive strength of 35.9 MPa. Compared with the traditional clinker producing process, energy consumption for producing activated coal gangue could save 90.7 kg/ton equivalently, which is due to its low calcination temperature at 800 °C and calorific value (about 6688 kJ/kg) of the coal gangue.