EDTA淋洗修复Cu污染土壤的去除效率与适宜淋洗剂用量的选取

Washing of Cu-contaminated Soil Using EDTA—Removal Efficiency and the Optimization of EDTA Dosage

采用批量淋洗实验方法,以乙二胺四乙酸二钠盐(EDTA-Na2)溶液修复某工业废弃地Cu污染土壤,研究了不同EDTA-Na2用量对重金属Cu的去除效果以及Ca、Fe等常量元素的释放特征。结果表明,在实验条件下,Cu的去除率随着EDTA-Na2用量的增加而提高,4.00 mol/kg时达到最大,同时随着EDTA-Na2用量的增加,Ca的释放量减少,Fe、Al等释放量增加;以土壤三级标准(GB15618-1995)作为修复目标,当EDTA用量为0.80 mol/kg时,淋洗后土壤中Cu基本达到三级标准;通过计算每摩尔EDTA洗出金属的摩尔数,发现EDTA对金属的洗出效率(摩尔比)随着淋洗剂用量的增加而下降;当采用0.80 mol/kg EDTA用量时,Cu/(K+Na+Ca+Mg+Fe+Al+Mn+Si)的摩尔比最大,继续增加EDTA用量,Cu/(K+Na+Ca+Mg+Fe+Al+Mn+Si)的摩尔比下降,表明较高的EDTA用量主要用于其他金属元素的释放。因此在本研究中0.80 mol/kg EDTA是适宜的淋洗剂用量,修复后土壤不仅可以达到土壤三级标准,而且相对于其他金属而言,对Cu的洗出效率最大。在化学淋洗修复中应根据土壤修复目标,结合金属的总去除率和EDTA对金属的洗出效率来选取适宜的淋洗剂用量。

In a series of batch washing experiments,EDTA solution was used to remediate Cu contaminated soil derived from a Brown Field Site to investigate the removal efficiency of Cu as well as the release characteristics of major elements（Ca,Fe and so forth） by the application of six different EDTA dosages（0.10～6.00 mol/kg）.Results showed that,with the increase of EDTA dosage,Cu removal efficiency was enhanced and reached a maximum at 4.00 mol/kg,accompanied by the decrease of Ca releasing and the increase of Fe and Al releasing.When 0.80 mol/kg EDTA was adopted,residual Cu concentration in the washed soil generally complied with the Environmental Quality Standard for Soils（Class Ⅲ）（GB15618-1995）.When calculating the amount of metals washed by per mole EDTA,it was found that the molal ratio of metals to EDTA in the eluate decreased accordingly with the increase of EDTA addition.The maximum molal ratio of Cu/（K＋Na＋Ca＋Mg＋Fe＋Al＋Mn＋Si） was obtained when 0.80 mol/kg EDTA was applied.However,this molal ratio decreased when the EDTA dosage was further increased,indicating that higher EDTA dosages were mainly used for the releasing of other metals.Thus,in this study,0.80 mol/kg EDTA was considered as the most appropriate dosage which could not only remediate heavy metals contaminated soil to meet the national standard,but also had the best removal efficiency of Cu when compared with other metals.Conclusively,the appropriate EDTA dosages should be determined on the basis of remediation aim,with the total metal removal efficiency and molal ratio of metals to EDTA being taken into account simultaneously.