Abstract:In order to investigate characteristics of heavy metals removal with chemical washing from soil which was considered as a heterogeneous system, the soil aggregate were screened and graded on particle sizes of 0.25-2 mm, 0.05-0.25 mm and <0.05 mm. Then the effects of EDTA, citric acid and ferric chloride (FeCl3) on aggregate structure, lead (Pb) and cadmium (Cd) concentrations and their speciation during washing were investigated. The results show that the removal rates of heavy metals in aggregates with different particle sizes were significantly different (P<0.05). Pb and Cd in small aggregates (particle sizes <0.05 mm) had higher removal rates than that in big ones. After washing, the proportion of residual state Cd on small aggregates increased, while the proportion of effective state Pb increased. After washing, the average diameter (WMWD) of the aggregates decreased by 77.25%, 80.98% and 49.15%, respectively, and the disintegration of water-stable aggregates may increase the specific adsorption capacity of soil to Pb and Cd. Compared with EDTA and citric acid, FeCl3 has lower structural damage to water-stable aggregates and better heavy metal leaching effect, which is beneficial to the subsequent safe reuse of soil.