Basic properties, characteristic heavy metals leaching and migration of coal incineration fly ash-based mortar

Abstract

Accumulation of fly ash causes waste of land resources and certain environmental pollution problems, mainly from coal incineration. As a result, to investigate the leaching, migration law, and environmental safety of these distinctive heavy metals, this study used representative fly ashes from two power plants as research objects to screen out the characteristic heavy metals and prepare and test mortar specimens. The results of the study show that after four heavy metal risk assessment methods, it was concluded that the characteristic heavy metals where are in A power plant’s fly ash were Hg, Cr, Pb and As, and in that of power plant B were Hg and As. The best fly ash admixture was 20% and the best water-binder ratio was 0.48, as learned from the compressive strength experiment. The heavy metal leaching test was done for block mortar and crushed mortar on the use of the best mix ratio. When compared to the raw materials, the specimens' heavy metal leaching content was significantly lower. And the heavy metals in crushed mortar were easier to leach. After the analysis of the migration transformation model, the heavy metals migrated downward in the mortar under the action of gravity. According to the one-dimensional diffusion model of Fick's second law, the migration of the various characteristic heavy metals was ranked from strong to weak as Pb, As, Cr, and Hg, and the ranking of the maximum safe age was ranged from large to small as Hg, Pb, Cr, and As. The findings of the study will provide fundamental theoretical support for the environmental safety risk posed by heavy metals and safety controls like the leaching of characteristic heavy metals in current fly ash-based mortar products. They will also provide further guidance on how to use fly ash as a resource.