Study on properties of representative ordinary Portland cement: Heavy metal risk assessment, leaching release kinetics and hydration coupling mechanism

As an important basic material in the construction industry, the potential harm of heavy metal elements contained in Portland cement (PC) to the ecosystem and human health cannot be ignored. In this research, PC from five representative areas of China was chosen to systematically research its heavy metal risk assessment, leaching release kinetics and hydration coupling mechanism using the advanced scientific testing techniques and research methods, so as to provide reasonable suggestions for the efficient, safe and environmentally friendly utilization of PC. The research indicated that the chemical constituents of PC are CaO, SiO2, Al2O3, Fe2O3, etc. The primary mineral composition were calcite, quartz, magnesite and mullite. Through the detection and analysis of the contents of Cr, As, Cd and Pb in PC, in accordance with the analysis results of environmental evaluation model, there were no obvious environmental risks of the four heavy metals, but the contents of Cr and Cd in PC need to focus on. At the same time, Cr in PC needs to be key-point controlled as human health risk assessments indicated that they posed a carcinogenic risk to the human body through oral administration. However, as the cumulative effect of As and Pb, their toxicity cannot be ignored in human health evaluation. Therefore, As and Pb need to be re-incorporated into the category of characteristic noxious heavy metals. But the control level was marked as medium; Cr and Cd control level was high.The fitting results of release kinetics showed that most of the heavy metal leaching in PC can be well fitted by Elovich model and second-order kinetic model. This indicated that Elovich model, second-order kinetic model and parabolic model were more worthy of study in the leaching release kinetics of heavy metals. In the meantime, the study showed that the leaching of heavy metals in PC was controlled by a series of effects such as parabolic model. On the basis of the dynamic model of heavy metal content in five kinds of PC with curing duration, the optimum safe age of noxious heavy metals in PC after PC hydration was explored. Through XPS test results, it was discovered that the Cr, As, Cd and Pb in PC present in the formation of Cr3+, Cr6+, As3+, As5+, Cd2+ and Pb4+. These noxious heavy metal ions were harmful to the human body by means of the infiltration and migration of soil and groundwater. Lastly, the hydration coupling mechanism of heavy metals in PC were discussed, and the content of characteristic heavy metals in PC under various usage scenes were limited.