Ultrasound-Enhanced Extraction Of Heavy Metals From Contaminated Soils

Due to it’s special acceleration effect to chemical reactions, ultrasound is applied to environmental pollution remediation, which attracts a more concern. In this study, heavy metal extraction experiments were conducted by using solutions of deionized water, hydrochloric acid (HC1), and ethylenediaminetetraacetic acid (EDTA) as extractants under three different conditions (ultrasound, vibrating, ultrasound-vibrating). And two extraction orthogonal experiments of heavy metals from a contaminated soil were conducted with ultrasound-enhanced HC1and EDTA solutions, and changes in species of Cd, Cu, Pb and Zn in the soil were analyzed using the BCR sequential extraction procedures before and after extraction. The main results are as follows:1)0.05mol·L-1HC1and0.05mol·L-1EDTA reached two orders of magnitude higher removal ratios for soil Pb, Cd, Cu, Zn than deionized water did; however, they both might lead to a raise of acid-extractable form of Pb, Cu and Zn.2) Ultrasound enhanced the remediation of soil reduced extracting time significantly. Using0.05mol·L-1HC1and0.05mol·L-1EDTA as extractants,10minutes of ultrasound irradiation could reach the similar effects of heavy metals removing from the soil as2hours of vibrating extraction. Under10min ultrasound-enhanced condition, the extraction ratios of soil Pb, Cd, Cu, Zn were30.54%,76.73%,17.59%and19.37%, respectively, for HC1, and78.05%,79.25%,43.07%, and21.74%, respectively, for EDTA. Ultrasound accelerated desorption of heavy metals from soil particles and raised the combination efficiency between deionized water/EDTA and heavy metals, but didn’t change the extraction order of Pb, Cd, Cu, Zn.3) The optimal condition for HC1extracting soil heavy metals under ultrasound-enhanced was:HC1concentration of100mmol·L-1, soil to liquid rate of1:5, irradiation time of20mins, ultrasound power of5%and extraction3times. Under this condition, removal ratios of soil Cd, Cu, Pb, and Zn were80.91%,82.19%,49.40%and51.93%, respectively. The optimal condition for EDTA extracting soil heavy metals under ultrasound-enhanced was:EDTA concentration of20mmol·L-1, soil to liquid rate of1:20, irradiation time of5mins, ultrasound power of1%and extraction3times. Under this condition, removal ratios of soil Cd, Cu, Pb, and Zn were78.02%,74.20%,51.59%and33.36%, respectively.4) Concentrations of extractants were one of important factor for heavy metals removing from soil. Removal ratios of soil heavy metals increased with increasing concentrations of HCl/EDTA solutions. The results of species analysis of heavy metals in the soil before and after extraction indicated that residual fraction of heavy metals were decreased significantly by using ultrasound-enhanced HCl/EDTA solutions.74.92%of residual Pb,82.64%of residual Cd,42.82%of residual Cu, and56.37%of residual Zn were removed out from the tested soil by HCl, and64.00%of residual Pb,56.76%of residual Cd,44.73%of residual Cu, and38.60%of residual Zn were removed out from the tested soil by EDTA in this experiment.