Analysis of the Microenvironment of Iron in an Alkalinated Fayalite‐Containing Copper Slag‐Inorganic Polymeric Network as a Function of Temperature by Spectroscopic Methods

Abstract Application of X‐ray diffraction, infrared spectra, UV–visible, and electron paramagnetic resonance spectroscopy to determine the microenvironment of iron in copper slag (CS) and alkali‐activated copper slag (CSG), subjected to heat treatment, is discussed in this study. An alkalinated iron‐rich copper slag was synthesized utilizing sodium water glass with a silica modulus of 1.1, cured at 80 °C, attaining a satisfactory compressive strength above 20 MPa at 28 days of curing age. The transformation of the octahedral Fe 2+ to tetrahedral Fe 3+ was confirmed by the appearance of the UV band at 233.0 nm in CSG. Upon thermal treatment, a declining trend in strength to an extent of 45% was observed till 400 °C in CSG and then a sharp gain of strength was noted up to 50% at 800 °C which is attributed to the thermally decomposed products of amorphous silica and iron oxide clusters. XRD reflections of hematite are observed in CSG, which is similar to the desilication of the fayalite phase in CS upon calcination. The structural transformation of tetrahedral symmetry or distorted form of Fe 3+ to a cluster of Fe 3+ was further confirmed by the shift in the EPR signal to decreased g‐factor. A clear UV sub‐band shift to the higher wavelength at greater than 450 nm is ascribed to oligomeric Fe 2 O 3 species. This study clearly shows that the isolated iron was converted into clusters, thereby increasing the thermal stability of the copper slag inorganic network.