Water treatment residue and coal fly ash geopolymers

Water treatment residue (WTR) from water purification is a non-hazardous solid waste commonly discharged in landfills. WTR contains aluminosilicates and can participate in geopolymerization. Due to the low alkaline activity of WTR, we used coal fly ash with the WTR to coal fly ash ratio from 80 wt% to 50 wt% and activated it with the 8M NaOH solution. The specimens were cured in normal conditions for 28 days at room temperature, and in an autoclave for 7 days under a pressure of 2 MPa and temperature of 215 ºC. The test results showed that the compressive strength of geopolymers cured in an autoclave reached 28.8 MPa, which is much higher than for those cured in normal conditions with only 13.2 MPa. The microstructure (XRD, SEM) and chemical bonding (FTIR) analyses confirmed the analcime crystal formation in the geopolymers.