土壤重金属的醋酸淋洗效果及其对地下水的影响评估

Efficacy of acetic acid leaching in removing heavy metals from soil and assessment of its effects on groundwater

为探究醋酸作为土壤化学淋洗剂去除重金属的效果和对环境的影响,采用土柱模拟耕层原位淋洗的方法,探究了0.8、1.0、1.5mol·L^(-1)3种浓度的醋酸对4种类型土壤中重金属的去除效果、迁移特性、形态变化,以及对土壤主要理化性质的影响。结果表明:醋酸淋洗对酸性和弱酸性污染土壤的重金属淋洗效果比较好,其中醋酸浓度在1.0 mol·L^(-1)以上时Cd的去除效果达到40%~60%,但对Pb、Cu、Zn的去除效果较差,各种醋酸浓度下去除率均低于20%。醋酸淋洗主要去除表层土壤中可交换态和可还原态的Cd,被淋洗的Cd在20~40 cm底土层部分截留。以1.0 mol·L^(-1)的醋酸淋洗土壤不会对土壤主要养分元素含量造成显著影响(P<0.05),但是淋出液Cd、Pb的浓度高于Ⅳ类地下水标准。因此,1.0 mol·L^(-1)为醋酸淋洗去除土壤Cd的较佳浓度,Cd含量低于0.6 mg·kg^(-1)的轻微污染酸性土壤可望达标,但是淋出液中Cd、Pb存在污染地下水的风险,实践中应当与深层固定等配套技术联用。

In order to elucidate the efficiency of acetic acid leaching in the removal of heavy metals from soil and its environmental impacts,we conducted a soil column leaching experiment that simulates in-situ flushing.We assessed the efficacy of three acetic acid concentrations(0.8,1.0 mol·L^(-1),and 1.5 mol·L^(-1)),and used four contaminated soils to assess the removal rate,downward migration characteristics,and changes in heavy metal speciation.The effects of acetic acid leaching on the main nutrient elements in soil were also investigated.The results showed that acetic acid leaching had a high removal efficiency for heavy metals in the acidic and slightly acid soils,particularly in the case of Cd,for which the removal rate reached 40%–60%at acetic acid concentrations of 1.0 mol·L^(-1) and higher.Comparatively,the removal of Pb,Cu,and Zn was relatively poor,at less than 20%.Acetic acid leaching mainly removed the exchangeable and reducible Cd from top-soil,which was partially retained in the 20–40 cm sub-soil layer.Leaching with acetic acid at 1.0 mol·L^(-1) had no significant effect on contents of the main nutrients in the top-soil(P<0.05),although the concentrations of Cd and Pb in the leachate were higher than the gradeⅣgroundwater standard limit.These results indicate that 1.0 mol·L^(-1) is the optimal acetic acid concentration for the leaching of soil Cd and could be used to effectively clean up slightly contaminated soils with Cd concentrations lower than 0.6 mg·kg^(-1).However,attention should be paid to the risk of groundwater pollution with Cd and Pb.In practice,of acetic acid leaching of contaminated soils should be combined with countermeasures such as sub-soil fixation.