冻融对污染场地土壤重金属稳定化性能的影响

Effects of Freeze-Thaw Cycle on Stabilization Performance of Heavy Metals in Soil of Contaminated Site

为了分析冻融对污染场地土壤重金属稳定化性能的影响,采用赤泥和硫化钠作为添加剂,对土壤中的Pb、Zn和Cd进行稳定化处理,并通过模拟冻融过程,分析冻融循环后重金属的浸出毒性、生物可给性、土壤p H和土壤结构的变化,探讨冻融循环对稳定化处理土壤中重金属长期稳定性能的影响.结果表明:稳定化处理后土壤中Pb、Zn和Cd的浸出毒性比原始供试土壤分别降低了98.5%、99.8%和99.7%.养护30 d后,稳定化处理土壤中Zn和Cd的生物可给性分别由28.8%、49.5%降至11.5%、21.8%,Pb的生物可给性由52.9%升至57.9%.经过30 d冻融循环后,冻融土壤中Pb、Zn和Cd的浸出毒性比原始供试土壤中相应重金属质量分数分别增加了4.27、2.47、89.65 mg/L.经过冻融循环后,土壤中重金属的生物可给性比未冻融土壤略有升高.随着养护时间和冻融时间的延长,土壤p H呈升高趋势.不同阶段土壤扫描电镜结果显示,冻融循环致使土壤空隙变大、结构松散,说明冻融循环对稳定化土壤结构有一定损伤.分析结果表明,冻融过程增加了Pb、Zn和Cd释放的环境风险.

In order to analyze the effects of freeze-thaw cycles on the stabilization performance of heavy metals,soils contaminated with Pb,Zn and Cd were stabilized using red mud and sodium sulfide as additives. Leaching toxicity and bioavailability of heavy metals were measured. Structure and p H of the soil were studied for investigating the long-term influence of freeze-thaw on the stability of Pb,Zn and Cd in the soils after the stabilization treatment. The results of toxic characteristic leaching procedure showed that the leaching toxicities of Pb,Zn and Cd decreased significantly,with percentages of 98. 5%,99. 8% and 99. 7%,respectively,compared with the original soil.The bioavailability extraction test indicated available parts of Zn and Cd were reduced from 28. 8% and 49. 5% to 11. 5% and 21. 8%after curing time of 30 days. The bioavailability of Pb was raised from 52. 9% to 57. 9%. The stability varieties of the three metals were analyzed after 30 day freeze-thaw cycles for forecasting the release characteristics; the leaching toxicities of Pb,Zn and Cd increased by4. 27,2. 47 and 89. 65 mg/L,compared with the original contaminated soil without freeze-thaw cycles. The bioavailability of heavy metals in the soils after freeze-thaw treatment was slightly higher than the corresponding content of pollutants in samples without freeze-thaw treatment. The p H value of soil increased with the extension of curing and freeze-thaw time. It could be seen clearly from scanning electron microscopy images that the soil gap became wider,and the soil structure looser,after the continuous freeze-thaw cycle.The results of qualitative and quantitative analysis indicated that the freeze-thaw process increased the release risks of Zn,Pb and Cd in the soil.