长期冻融循环下固化铅锌镉复合重金属污染土抗剪强度及浸出特征研究

Shear strength and leaching characteristics of solidified lead-zinc-cadmium composite heavy metal contaminated soil under long-term freeze-thaw cycles

为了评估长期冻融循环后(最长90d(次))固化复合重金属污染土的的抗剪强度及浸出特征,采用水泥、生石灰和粉煤灰按比例混合的复合固化剂固化/稳定化铅锌镉复合重金属污染土进行三轴压缩试验及毒性特征浸出程序试验.结果表明,固化污染土体的内摩擦角仅在冻融循环3次内有明显增加,增加率高达96.3%;粘聚力在冻融循环30次内总体趋势不断下降,之后无显著变化,最终下降率达到54.23%;Pb^(2+)、Zn^(2+)、Cd^(2+)浸出浓度与冻融循环次数呈正比;EC值与冻融循环次数在总体上正相关;长期冻融循环作用后浸出液的pH值降低.并通过扫描电子显微镜,进一步探究长期冻融循环下固化污染土抗剪强度及浸出特征的劣化机理,结果显示在冻融循环后期固化土体内生成了大量的延迟钙矾石,这些延迟钙矾石在形成过程中的膨胀作用是引起抗剪强度损失、重金属浸出浓度升高的主要原因.

In order to evaluate the shear strength and leaching characteristics of the solidified composite heavy metal contaminated soil after long-term freeze-thaw cycles(up to 90days(times)),triaxial compression test and toxicity characteristic leaching procedure test were carried out on the lead-zinc-cadmium composite heavy metal contaminated soil after solidification/stabilization with composite curing agent of cement,quicklime and fly ash.The results show that the angle of internal friction only increased significantly to 3 freeze-thaw cycles,and the increase rated was as high as 96.3%;while the overall trend of cohesion continued to decline by 30 freeze-thaw cycles,and there was no significant change afterwards,and the final decline rate reached 54.23%;the leaching concentration of Pb^(2+),Zn^(2+),Cd^(2+),and the EC value of the extract is proportional to the number of freeze-thaw cycles;the pH value of the extract decreases after long-term freeze-thaw cycles.And through scanning electron microscopy,we further explored the degradation mechanism of the shear strength and leaching characteristics of solidified contaminated soil under long-term freeze-thaw cycles.The results show that a large amount of delayed ettringite is formed in the solidified soil at the end of the freeze-thaw cycle,and its expansion during the formation process is the main reason for the loss of shear strength and the increase of heavy metal leaching concentration.