Utilization of fly ash as building material admixture: Basic properties and heavy metal leaching

Abstract

The potential harm to the environment and human body caused by heavy metal elements such as Cd, Cr, Pb in fly ash cannot be ignored. In this study, microscopic analysis and heavy metal hazard analysis were performed on fly ash samples from four regions in China. XRF, XRD, FTIR and SEM/EDS test results showed that the main components of fly ash are Si, Ca, Al, O and other elements, and the main mineral components are mullite, quartz and amorphous aluminosilicate. The results showed that six heavy metal elements of As, Hg, Cd, Cr, Pb and Ni from the EDS test charts of these four types of fly ash. Based on the detection of the six heavy metal contents in fly ash, the results of the pollution evaluation of these four types of fly ash were consistent according to the single factor index, potential ecological risk index, and index of geo-accumulation. This indicated that Cd/Hg in FA 1, FA 2 and FA 3 has a high risk of environmental pollution. In the meantime, Cr and As in fly ash need to be controlled, because the human health risk assessment showed that they will bring carcinogenic risk to the human body through oral intake. The study on the migration law of characteristic heavy metals by taking FA 4 as an example showed that the leaching rate of Cr, Hg and Cd decreased with the increase of grinding particle size. Among the three characteristic heavy metals, mercury had the highest leaching rate. From the XPS detection results of FA 4, it was found that the valence states of these three heavy metals in FA 4 are Cr3+, Cr6+, Cd2+, Hg2+ respectively. These harmful heavy metal ions gradually enter the deep soil and groundwater through osmosis. Finally, based on the control model constructed in this study, the contents of these three heavy metals in fly ash in different application scenarios were limited.