不同pH淋滤条件下飞灰中铬、锌、镍、铅的环境效应

粉煤灰是煤炭燃烧后的副产物，富集于粉煤灰中的微量元素在风化、淋溶等外力作用下极易释放到环境中。pH是影响微量元素淋滤行为的重要因素，利用室内砂箱仿真模拟试验研究不同pH淋滤条件下粉煤灰中微量元素的迁移行为具有重要意义。研究结果表明：不同pH条件淋滤后的粉煤灰中Cr、Zn、Ni和Pb的含量都降低。淋滤后水体中Cr的浓度随着pH的升高呈先增大后减少的趋势，在pH为10时达到峰值；Zn、Ni和Pb的浓度随着pH的升高均呈现先减小后增大的特征。淋滤后土壤中Cr元素含量随pH值的升高表现为先减小后增大；Zn、Ni和Pb含量的变化趋势相似，在pH值为2—6.8时减小，随着pH值的继续升高，在pH为10左右达到峰值，随后下降。粉煤灰在短期淋滤条件下对土壤生态环境影响较小，一般情况下可以忽略。

Environmental effects of chromium, zinc, nickel and lead in fly ash under different pH leaching conditions

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.