Abstract: Background, aim and scope Fly ash is a by-product of coal combustion, and trace elements enriched in fly ash are easily released into the environment under external forces such as weathering and leaching. pH is an important factor affecting the leaching behavior of trace elements. Therefore, it is of great significance to study the migration behavior of trace elements under different pH leaching conditions using indoor sand box simulation experiments. Materials and methods The fly ash used in the test was collected in a power plant in Hefei and the soil was collected in the garden on campus. Simulation tests of indoor sandbox were carried out under five different pH leaching conditions.The leachate (simulated groundwater), soils and fly ash samples were collected after 24 h leaching, then the contents of trace elements contained in them were determined. Results The results demonstrated that the contents of Cr, Zn, Ni and Pb in fly ash were all reduced and the Cr, Zn, Ni and Pb elements were enriched in different degrees in soil after leaching. Discussion Zn, Ni and Pb are cationic elements, while Cr exists in the form of cations and anions. Acid condition can promote the release of cationic trace elements in fly ash. As pH continues to rise, it is advantageous to hydrolysis of metal ions or formation of hydroxyl complexes. Due to the adsorption, enrichment, migration and transformation of trace elements in soil, the trace elements enriched in soils may contaminate environment. Conclusions After leaching, the concentration of Cr in the groundwater increased first and then decreased with the increase of pH, and reached the peak at pH 10. The concentrations of Zn, Ni, and Pb decreased first and then increased with increasing pH. After leaching, the content of Cr in soil decreased first , then increased with the increase of pH value. The contents of Zn, Ni, and Pb showed a similar change trend, decreased in the pH range of 2 to 6.8, and reached its peak at around pH 10, then fell as the pH continued to rise. Fly ash has little effect on soil ecological environment under the condition of short-term leaching, and it can be neglected in general. Recommendations and perspectives This study illustrates environmental effects of Cr, Zn, Ni and Pb in fly ash under different pH leaching and provides a scientific basis for the safe, stable and sustainable utilization of fly ash.
Keywords: coal fly ash; leaching behavior; pH; trace element