多硫化钙对铬污染土壤处理效果的长期稳定性研究

Study on long-term stability of the treatment of Cr-contaminated soil by using CPS

稳定化修复技术逐渐成为我国现阶段重金属污染土壤修复的主要技术,其修复后验收主要通过分析土壤重金属的浸出浓度来评价修复效果,然而该验收指标未反映土壤重金属在不同情景下的长期稳定性.本研究以经稳定化药剂多硫化钙(CPS)处理前后的某电镀厂铬(Cr)污染土壤为对象,开展多pH浸出、模拟酸雨淋溶、冻融循环和干湿交替作用下土壤重金属Cr的长期稳定性研究.结果表明:在多pH浸出实验中,稳定化处理后达标土壤(CPS-D-3)在pH大于6.92时,Cr(Ⅵ)浸出浓度大于0.05 mg·L^(-1).在整个试验模拟酸雨淋溶作用的过程中(30年),稳定化处理可以有效抑制Cr向环境中释放,CPS-D-3中的总Cr和Cr(Ⅵ)的累积释放量比未经稳定化处理的Cr污染土壤(CPS-D-1)分别显著减少了91.86%和99.61%.在冻融循环的过程中,稳定化处理可有效降低土壤中浸出总Cr的含量.经过15次干湿交替后CPS-D-1和CPS-D-3分别比未经过干湿交替作用时浸出总Cr浓度减少了99.96%和96.88%.多pH浸出试验可以作为检验土壤安全的较为敏感的指标,冻融循环、模拟酸雨淋溶和干湿交替评估方法可协助评价重金属的长期稳定性.

Stabilization has become one of the main viable technologies for remediation of heavy metal contaminated soil. At present,the restoration is mainly conducted by determining heavy metal leachates in the soil leaching solution after a short term. However,it cannot fully reflect the stability of heavy metals in soil for longer time and under different natural environments. The objective of current is to investigate the effects of excessive pH leaching,simulated acid rain leaching,freeze-thaw cycles and wet-dry cycles on the stabilization of Cr contaminated soils before and after calcium polysulfide（CPS） treatment. The results showed that for the pH values greater than 6.92,leaching concentration of Cr（Ⅵ） remained higher than 0.05 mg·L^-1 in CPS-D-3 During the whole period of acid rain leaching,simulated for almost 30 years,stabilizing treatment could effectively inhibit the release of Cr into the environment,the cumulative release amounts of total Cr and Cr（ Ⅵ） distinctly decreased to 91.86% and 99.61% in CPS-D-3,respectively,compared to CPS-D-1. In the process of freeze-thaw cycles,stabilization treatment can effectively reduce the leaching content of total Cr in soil. After 15 times of wet-dry cycles,the total Cr leaching toxicity for CPS-D-1 and CPS-D-3 respectively decreased by 99.96% and 96.88% compared to the untreated soil. The excessive pH leaching was used as a sensitive indictor to test the soil safety. Moreover,freeze-thaw cycles,simulated acid rain leaching and wet-dry cycles proved helpful in evaluating the long-term stability of heavy metals.