淋洗对农田土壤镉铅锌的去除、移动性和有效性的影响

Impact of soil washing on Cd,Pb and Zn removal,mobility and availability for farming soil

以福建省Cd-Pb-Zn矿区周边的农田污染土壤为材料,通过室内连续振荡淋洗和ICP-MS测定,研究了4种常用的淋洗剂(柠檬酸、EDTA、FeCl_3和HCl)一次和连续5次淋洗对土壤Cd、Pb和Zn的去除效果,及对其形态、移动性和有效性的影响。结果表明,与一次淋洗相比,连续5次淋洗能够增加这4种淋洗剂对Cd、Pb和Zn的去除效果,FeCl_3、EDTA和柠檬酸分别对Cd、Pb和Zn的去除效果最好,5次淋洗后分别达到89. 29%、24. 95%和36. 72%。BCR形态分析结果表明,4种淋洗剂对土壤Cd和Zn的淋洗主要是通过对弱酸提取和可还原态的Cd和Zn去除而实现的;对于土壤Pb的淋洗主要是对可还原态Pb的去除;对可氧化态和残余态重金属影响不大。其次,淋洗可导致土壤Cd、Pb和Zn移动性和有效性的增加,从而会增加其生态环境风险而导致淋洗效果的丧失,在评价淋洗效果时应予以关注。最后,从淋洗前后土壤重金属有效态变化角度考虑,对Cd-Pb-Zn复合污染土壤,EDTA是较好的淋洗剂选择。

The paper is inclined to make an investigation and examination of the effets of the soil washing on the heavy metals(Cd,Pb and Zn)removal from the Cd-Pb-Zn contaminated farmlands nearby a Pb-Zn mining area in Fujian Province.For the research purpose,we have chosen 4 commonly used reagents as washing extractants,that is,the citric acid(CA),the ethylenediaminetetraacetic acid(EDTA),the hydrochloride acid(HCl)and the ferric chloride(FeCl3).To make our study more purposeful and effective,we have managed to conduct 5 successive rounds of laboratory washing of Cd,Pb and Zn contaminants by oscillating washing for the effectiveness of single round,and managed to account and measure the contents of Cd,Pb and Zn in the leacheate by the inductively coupled plasma mass spectrometry(ICP-MS).The European Community Bureau of Reference(BCR)sequential extraction was used to assess the redistribution of Cd,Pb and Zn between the fractions before and after washing.Additionally,changes of soil Cd,Pb and Zn mobility and availability(DTPA-extracted)were also assessed.The results of our experimental study proved that the 5 successive washing rounds has successfully removed more metal contaminants than those of the single round washing.The best removal efficiency with FeCl3,EDTA and citric acid from the contaminatedsoil could reach 89.29%of Cd,24.95%of Pb and 36.27%of Zn through a series of 5 successive washing rounds,respectively.The results of BCR sequential extraction demonstrated that the Cd and Zn removal with the 4 commonly used washing extractants tend to remove mainly from exchangeable/acid extractable(F1)and easily reducible fraction(F2),respectively.However,Lead(Pb)has been mainly removed form the easily reducible fractions,though no significant impact has been detected on the oxidizable(F3)and residual fraction(F4)of Cd,Pb and Zn as a result of the soil washing.Moreover,the results also verified that the soil washing could lead to the increase of Cd,Pb and Zn mobility and availability in the soil so as to aggrevate their ecoenvironmental risk and the loss of washing effects.Therefore,greater attention has to be paid to the evaluation of the washing effects.And,finally,from the point of view of availability,it is recommanded to take EDTA as the alternative of the washing extractant for the Cd-Pb-Zn contaminated farm land soil.