Migration and solidification behavior of the semivolatile heavy metal elements Zn and Cd during high ferrite cement clinker (HFCC) calcination.

The use of solid waste to produce low carbon, high ferrite cement clinker (HFCC) with favorable durability delivers potential application prospects. However, the semivolatile heavy metals Zn and Cd in solid waste not only restrict its utilization ratio but also cause potential environmental pollution. In this study, the migration and solidification behavior of Zn and Cd during calcination and their action mechanisms on phase reconstruction are systematically studied. The reaction sequence and conditions of Zn were revealed by experimental tests and phase diagram simulation. Zn2+ will firstly solidify in the C 2 S phase by the solid-phase reaction. After liquid phase forms, Zn2+ is more inclined to substitute Fe3+ in the C 4 AF phase with 4-coordination in the [FeO 4 ]. Only a small amount of Zn2+ enters the C 3 A and C 3 S phases in the form of interstitial solid solution. Zn promotes the formation of the liquid phase and C 3 S phase. And HFCCs indicate a favorable solidification effect on Zn. While due to low volatilization temperature and high volatility of Cd, even at a low sintering temperature, the HFCC cannot greatly reduce the volatilization of Cd. Cd2+ mainly exists in HFCC by substituting Ca2+ in the C 3 S, C 2 S and C 4 AF phases with a 6-coordination number in [CaO 6 ] to form the spatial configuration of octahedral complexes. • Reaction sequence and reaction condition of Zn during sintering were revealed. • Compared with OPC, high ferrite cement clinker (HFCC) has a stronger solidification ability for Zn. • Solidification priority depends on liquid phase content, elements volatilization and lattice distortion. [ABSTRACT FROM AUTHOR]