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