化学淋洗对土壤团聚体稳定性及其重金属赋存形态的影响

为探究重金属在土壤非均质体系中的淋洗特性,分别考察了3种化学淋洗剂乙二胺四乙酸(EDTA)、柠檬酸和三氯化铁(FeCl_3)等对粒径为0.25～2.00 mm、0.05～0.25 mm和0.05 mm的土壤团聚体淋洗过程中团聚体结构、重金属Pb和Cd质量分数及其赋存形态影响。结果表明,不同粒径团聚体中重金属的淋洗效率存在显著差异(P0.05),小粒径(0.05 mm)的团聚体上Pb和Cd具有更高的淋洗效率。淋洗后较小粒径团聚体上残渣态Cd所占比例升高,但有效态的Pb所占比例增加。淋洗后团聚体的平均直径分别减小了77.25%、80.98%和49.15%,团聚体解体可能增加土壤对Pb和Cd的专性吸附能力。淋洗剂FeCl_3相较于EDTA和柠檬酸,对水稳性团聚体具有较低的结构破坏作用,同时具有较好的重金属淋洗效果,有利于土壤后续的安全再利用。

Effects of chemical washing on the stability of soil aggregates and the form of heavy metals

In order to investigate the characteristics of heavy metal removal with chemical washing from soil which was considered as a heterogeneous system, the soil aggregates were screened and graded on particle sizes of 0.25 mm to 2.00 mm, 0.05 mm to less than 0.25 mm and less than 0.05 mm. Then the effects of EDTA, citric acid and ferric chloride (FeCl₃) on the aggregate structure, the mass fraction of lead (Pb) and cadmium (Cd) and their speciation during washing were investigated. The results show that the removal rates of heavy metals in aggregates of different particle sizes were significantly different (P<0.05). Pb and Cd in small aggregates (particle sizes less than 0.05 mm) had higher removal rates than that in large aggregates. After washing, the proportion of residual state Cd on small aggregates increased, but the proportion of effective state Pb also increased. After washing, the average diameter of the aggregates of the three different particle sizes decreased by 77.25%, 80.98% and 49.15%, respectively. The disintegration of water-stable aggregates might increase the specific adsorption capacity of soil to Pb and Cd. Compared with EDTA and citric acid, FeCl₃ had lower structural damage to water-stable aggregates and better heavy metal leaching effect, which was beneficial to the subsequent safe reuse of soil.