重金属高污染农田土壤EDTA淋洗条件初探

Research on the Wash Condition Using EDTA for a Heavy Metal Severely Contaminated Agricultural Soil

通过室内振荡淋洗试验研究了乙二胺四乙酸二钠(EDTA)浓度、淋洗时间、液固比、淋洗次数对甘肃省白银市某高污染农田土壤中重金属去除效果的影响,并测定了EDTA淋洗前后土壤中重金属形态的变化。结果表明:淋洗剂浓度和液固比越高、淋洗时间越长、淋洗次数越多,对重金属的去除效果越好。在EDTA浓度为5 mmol/L、液固比为2.5、连续振荡淋洗3次、每次1 h时,对土壤中Cd、Cu、Pb、Zn 4种重金属的总去除率分别为55.2%、21.9%、19.3%和20.9%,其中Cd淋洗效率最高。EDTA对土壤中交换态、碳酸盐结合态和铁锰氧化物结合态重金属的去除效果明显,但不能有效去除有机及硫化物态和残余态土壤重金属。

Batch leaching experiments were conducted to examine the effects of different EDTA concentrations,washing duration,liquid/solid ratios and washing cycles on the removal of heavy metals in a contaminated agricultural soil from Baiyin City,Gansu Province,and the fractions of heavy metals in tested soils were determined before and after EDTA washing.The results showed that EDTA washing effect was much effective with high concentration and liquid/solid ratios,long washing duration and more washing cycles in general.Considering the feasibility on sites,a series of washing parameters were selected,it was 5 mmol/L of EDTA,liquid/solid ratio 2.5 and 3 times of successive washing cycles with 1 h for each.The removal rates of tested heavy metals under the selected condition were 55.2％ for Cd,21.9％ for Cu,19.3％ for Pb and 20.9％ for Zn,respectively.The results indicated that soil washing with EDTA was an efficient method to remove heavy metals from agricultural soil.Sequential fractionations of treated and untreated soil samples showed that EDTA was effective in removing the exchangeable,carbonate and oxide forms of Cd,Cu,Pb,and Zn,but ineffective for the organic and residual forms of test heavy metals.