The Washing Remediation Of The Contaminated Soil By Heavy Metals With IDS

The traditional washing reagents usually are disbiodegradable and can not efficiently remove heavy metals from the contaminated soil. A green chelator named Iminodisuccinic acid(IDS) was used as the washing reagent for washing remediation of the soil contaminated by heavy metals in this paper.The results of batch washing experiments showed that IDS could greatly enhance the desorption and elution of the heavy metals from the artificially-contaminated soils. For three contaminated soils by heavy metal with the concentration of 5mmol/kg, the presence of 10 mmol/L IDS significantly enhanced the extraction Cd, Cu, and Pb with the removal efficiencies of 63%, 85%, and 67%, respectively, after a 24-hour washing. Furthermore, the removal efficiencies of Cd, Cu and Pb could reach 98%, 78% and 94%, respectively, after five one-hour washing with 10 mmol/L IDS washing reagent. The washing removal of heavy metals from soils were effectively influenced by many factors, such as IDS concentration, pH value of solution, liquid/solid, reaction time and temperature. The results of the comparison with other washing reagents showed that heavy metals removal effectiveness of IDS was higher than that of oxalic acid and citric acid, but less than that of EDTA.The removal mechanism of IDS washing was studied through the fractions analysis of heavy metals in soil. To determine the effect of IDS on the different fractions of heavy metal, the sequential extractions were carried out before and after soil washing. The results showed that extraction capabilities of IDS to various metal fractions were very different, the extraction of the weak-acid extracted heavy metals were the most effective, and other fractions of heavy metals showed different leach abilities.Heavy metals such as Cd, Cu, and Pb, could be effectively removed from the eluates by precipitaion with Na2 S, and many factors, such as pH and [Na2S] / [IDS], have significant influence on the removal of heavy metals. When [Na2S] / [IDS] = 4: 1 and pH≥9, more than 90% of Cd, Cu, and Pb in the eluent could be removed and the recycled eluent still has higher removal capacity for heavy metal.The pilot test of the soil washing were implemented with a self-developed washing equipment in the optimal washing conditions obtained in laboratory. The results of the pilot test showed that the best performance of the removal of heavy metal from soil achieved in laboratory experiments could be realized in the pilot test after washing for five times, the presence of IDS could greatly enhance the extraction of Cd, Cu and Pb,and the removal efficiencies were 97.2%, 84.3% and 93.1%, respectively.