螯合剂和鼠李糖脂联合淋洗污染土壤中Cd

采用pH为4.31的土壤,制备3种Cd浓度水平的模拟污染土壤,研究了螯合剂和鼠李糖脂对土壤中Cd的淋洗特征,探讨了乙二胺四乙酸二钠(EDTA)和鼠李糖脂联合淋洗土壤中Cd的形态变化。结果表明,在淋洗剂浓度为0.025 mol·L~(-1)、初始pH为7时,EDTA、乙二胺二琥珀酸(EDDS)和柠檬酸(CIT)淋洗分别在220、140、60 min达到平衡,EDTA的淋洗效果最好,其对0.38、0.69、0.93 mg·kg~(-1)Cd污染土壤的最大淋洗率分别达到93.16%、93.62%和94.09%;淋洗过程符合准二级动力学模型,淋洗速率常数表现为0.38 mg·kg~(-1)Cd污染土壤0.69 mg·kg~(-1)Cd污染土壤0.93 mg·kg~(-1)Cd污染土壤。当EDTA和鼠李糖脂(浓度均为0.025 mol·L~(-1))的体积比为1.5∶1时,3种土壤中Cd的淋溶率分别为85.45%、89.25%和93.88%,淋洗平衡时间为50 min。EDTA和鼠李糖脂联用能够有效淋洗污染土壤中的交换态、碳酸盐结合态和有机结合态Cd,可能的作用机制是EDTA的螯合作用和鼠李糖脂的胶束增溶作用产生的协同效应。

Leaching characteristics of Cd in the contaminated soils with chelates and rhamnolipid

The simulated pollution soils with three Cd concentration levels were prepared, the leaching characteristics of Cd from the soils were studied with chelates and rhamnolipid, and the speciation variations of Cd in soil during the joint leaching process with EDTA and rhamnolipid was also discussed. When the eluent concentration was 0.025 mol·L^-1 and the initial pH was 7, the leaching process reached equilibrium at 220, 140 and 60 min with EDTA, ethylenediamine disuccinic acid(EDDS) and citric acid, respectively. The best leaching results could be obtained with EDTA, and the maximal leaching percentages were 93.16%, 93.62% and 94.09% for 0.38, 0.69 and 0.93 mg·kg^-1 Cd contaminated soils, respectively. The leaching process with EDTA could be described by pseudo two-order kinetic model, and the leaching rate constant showed a decreasing order of 0.38 mg·kg^-1 Cd contaminated soil, 0.69 mg·kg^-1 Cd contaminated soil and 0.93 mg·kg^-1 Cd contaminated soil. When the volume ratio of EDTA and rhamnolipid(0.025 mol·L^-1) was 1.5:1, the leaching percentages reached 85.45%, 89.25% and 93.88% for the three contaminated soils, respectively, and the leaching equilibrium time decreased to 50 min. Joint leaching can effectively release the exchangeable, carbonate bound and organic bound Cd in the contaminated soils, and the possible mechanism is the synergistic effect of EDTA chelation and the micellar solubilization of rhamnolipid.