超声辅助乙二醇双(2-氨基乙基醚)四乙酸洗脱土壤重金属及环境风险削减评价

Ultrasonic assisted ethylenebis(oxyethylenenitrilo) tetraacetic acid washing of heavy metal contaminated soil and assessment of environmental risk reduction

采用超声辅助乙二醇双(2-氨基乙基醚)四乙酸(EGTA)淋洗修复重金属污染土壤,结果表明,超声辅助EGTA对Cu和Cd的洗脱效果较好,对Zn和Pb的洗脱能力较弱,增加液固比可显著提高淋洗效果,增加超声时间和功率的效果则相对较小.淋洗处理后Cu、Zn和Cd浸出浓度减小,Pb浸出浓度增加.构建综合考虑土壤重金属残留量、浸出浓度和毒性的环境风险指数对修复效果进行评价,考察了EGTA投加量、液固比、超声时间以及超声功率等淋洗条件对重金属去除率和环境风险削减率的影响,并进行模拟和优化.当淋洗条件为EGTA投加量1.7 g·L-1、液固比10、超声时间40 min、超声功率600 W时,环境风险削减率预测值为79.7%,实测值为78.0%.可还原态Cu残留量、弱酸提取态Pb残留量和可还原态Zn残留量显著减少,弱酸提取态Zn残留量显著增加,而Cd各不同形态组分残留量均显著减少.超声辅助EGTA淋洗可有效削减Cu和Zn环境风险,但显著提高了Pb环境风险,EGTA投加量过高还可能提高Cd的环境风险.因此不适用于Pb污染土壤修复,用于Cd污染土壤修复时需管控其可能产生的二次污染风险.

The heavy metal contaminated soil was remediated by ultrasonic-assisted ethylenebis(oxyethylenenitrilo)tetraacetic acid(EGTA)washing.Results showed that ultrasonic-assisted EGTA washing had high reduction efficiency of copper(Cu)and cadmium(Cd),but had weaker washing capacity of zinc(Zn)or lead(Pb)in soil.Increasing liquid-solid ratio significantly improved the reduction rates of heavy metals,while increasing ultrasonic time and power revealed a relatively weak effect.After washing treatment,the leaching concentrations of Cu,Zn and Cd decreased,while that of Pb increased.An environmental risk index covering residual concentrations in soil,leaching concentrations and toxicity of heavy metals was constructed.The method was used to evaluate the effects of EGTA dosage,liquid-solid ratio,ultrasonic time and power on removal of each heavy metal and reduction rate of total environmental risk,and then the simulation and optimization of these effects were also conducted.The predicted value of the environmental risk reduction rate was 79.7%,and the measured value reached 78.0%with the condition of EGTA dosage 1.7 g·L-1,the liquid-solid ratio 10,ultrasonic time 40 min,and ultrasonic power 600 W.Under this condition,the concentration of residual Cu,the weak acid extractable Pb and the Zn in reducing fraction decreased significantly,the weak acid extractable Zn concentration increased significantly,and the residual Cd in all fractions decreased significantly.Overall,ultrasound-assisted EGTA washing can effectively reduce the environmental risks of Cu and Zn,but significantly increase the environmental risk of Pb.On the other hand,excessive EGTA dosage may also increase the environmental risk of Cd.Thus it is not suitable for the remediation of Pb contaminated soil.For Cd contaminated soil,it is also necessary to control the potential secondary pollution risk.