High ferrite cement clinker doped with PbO: Solidification and hydration behaviors

Solid wastes have become used to manufacture high ferrite cement clinker (HFCC). However, the behavior and effect of common heavy metal in solid wastes, i.e., lead during calcination process are still lacking. And understanding the solidification behavior of lead and its action mechanisms on phase reconstruction and hydration processes is crucial for rational utilization of lead-containing solid waste. Hence in this study, the distribution and solidification form of lead during HFCC calcination are explored and the effect of solidified lead in clinker on mineral phase composition, liquid phase properties, microstructures, and hydration properties of HFCC are systematically studied using various experimental and modelling methods. Results indicate that nearly all the Pb ions are solidified in the inherent phase structures, among which the majority are dissolved in the silicate phase. Due to the unstable phase configurations formed by lead substitution and the unmatched electronic structure, the Pb elements are subject to enter C3S, C2S, and C(4)AF in the form of interstitial solid solution. The solidification preference of the Pb element in the single crystal is C2S > C(4)AF > C3S as a result of the larger interstitial voids of C2S. The solidified Pb elements in HFCC mainly affect the mineral phase composition by varying the liquid phase properties. The formation of a eutectic mixture reduces the viscosity and formation temperature of the liquid phase, resulting in an increased interstitial phase content. Additionally, the high-energy-activated state of the Pb-formed interstitial solid solution increases the hydration activity of HFCC and the Pb elements in the voids of the tetrahedral silicate phase will not be released through chemical bond rupture. Thus, the solidification of Pb ions in clinker accelerates the hydration reaction of HFCCs and eventually leads to a higher ultimate hydration heat and the postponing effect on induction period is relatively low.