Removal of heavy metals and PAH from contaminated soil by chemical enhanced soil flushing/washing and advanced oxidation processes

As a consequence of the increasing concern about soil contamination, research on soilremediation technology has grown rapidly. The effects of the chelant dosage, solution pH, soil-to-solution ratio and the dissolved/soil organic matter on metal extraction with the application of ethylene-diamine-tetraacetic acid (EDTA) and [S,S]-stereoisomer of ethylenediaminedisuccinic acid (EDDS) mixture (including individual additions) were investigated through batch and column studies. In addition, soil contaminated with both heavy metals and organic pollutants are commonly found and often require extra effort for remediation. The effectiveness and mechanisms of heavy metal and naphthalene co-removal from artificially contaminated soil by FeEDTA/FeEDDS-activated persulfate were investigated, again through batch studies. Compared with Cu extraction, Pb and Zn extraction exhibit different kinetic behaviors at varying EDDS-to-metal molar ratios (under EDDS deficiency conditions) within two days. The extracted Pb and Zn were readily re-adsorbed onto the soil surfaces over time until reaching an apparent equilibrium between extraction and re-adsorption. In contrast, no re-adsorption occurred for Cu due to its high preference for forming complexes with EDDS. An alkaline pH range was preferable for Pb extraction when the EDDS was deficient, whereas the influence of varying the soil-to-solution ratio under EDDS deficiency was marginal compared with that of the EDDS-to-metal molar ratio and solution pH. Higher Pb extraction by EDDS and EDTA mixture was found compared with individual additions of EDDS or EDTA under chelant deficiency conditions. It appears that the EDDS and EDTA mixture can be utilized for metal extraction in a more efficient way according to their respective affinity towards particular metals, in which Pb is primarily complexed with EDTA, while Cu and Zn bind with both EDTA and EDDS. The synergistic performance of the EDDS and EDTA mixture probably resulted from the chan