Effect of Fe2+/Fe3+ on high-strength ceramsite prepared by sintering geopolymers using iron ore tailings

Iron ore tailings (IOTs) and coal gasification slag (CGS) were used to prepare novel ceramsites via high-temperature sintering. The IOTs were activated by NaOH to form a geopolymer that was sintered at 650 °C, 850 °C, and 1050 °C to obtain ceramsites. The formation of the geopolymer was confirmed by the characteristic peaks of Si–O–T (T = Si, Al) in the Fourier transform infrared spectra. X-ray diffractograms showed that Fe3+ participated in the geopolymerization reaction, whereas Fe2+ did not; hence the effect of the Fe2+/Fe3+ ratio was investigated. This ratio increased with increasing sintering temperature, thereby facilitating nucleation within the sample. The mullite–pyroxene network that formed upon sintering at 1050 °C improved the strength of the prepared ceramsite and its structure became more compact. Specifically, the cylinder compressive strength increased from 10.5 to 35.5 MPa after sintering at 1050 °C. Overall, this method of preparing high-strength ceramsites from IOTs and CGS can be used for the preparation of high-strength lightweight concrete.