Solidification mechanisms of copper in ferrite-rich Portland cement and its action mechanism in mineral phase

Abstract

High-ferrite Portland cement (HFPC) possesses favorable properties compared with ordinary Portland cement. Thus, it is promising to use solid waste for preparing the HFPC. Owing to the potential hazard of heavy metal copper in solid waste, the utilization of copper-containing solid waste in preparation of the ferrite-rich Portland cement has been restricted. This study aims to explore the migration and transformation law and solidification mechanisms of copper in ferrite-rich Portland clinker as well as its action mechanism in the mineral phase by using various experimental methods. Results show that copper element is well solidified in ferrite-rich Portland clinker. With the increase of CuO dosage, the formations of the C4AF phase and new phase, CaCuO2, in ferrite-rich Portland clinker are promoted, which are beneficial to improving the burnability of ferrite-rich Portland cement. Besides the phase of CaCuO2, the copper in clinker with 3 wt% CuO also appears in the form of Cu2O. According to the BSE-EDS analysis coupled with statistical analysis of copper atoms in the silicate phase and interstitial phase, the copper in ferrite-rich Portland clinker is proved to be preferentially solidified in C4AF. The added Cu2+ replaced the Fe3+ in C4AF and formed a continuous solid solution. Then the superseded Fe3+ is recombined with Al2+ to form more C4AF, which finally retards the formation of C3A. For the action mechanism of copper in silicate phases, it is proved that due to copper addition the coalescence probability of adjacent C3S grains will be substantially improved, which finally results in the enlargement of C3S grain. Meanwhile, a relatively large amount of copper addition shows an obvious retarding effect on the hydration process and a weakening effect on the hydration degree and strength of ferrite-rich Portland cement.