铅锌厂周边农田重金属污染土壤的化学淋洗修复及其应用潜力初探

发布时间：2018-08-21 15:07

【摘要】：近年来,随着采矿和冶炼业的迅速发展,在有色金属冶炼过程中排放的含有重金属的废渣、废液和废气会通过各种途径进入土壤,致使周边土壤生态系统遭到破坏,土壤环境质量下降。土壤环境的安全不仅关系到整个生态环境安全,而且对国家农业生产安全也至关重要。在众多污染土壤修复技术中,淋洗法因具有能迅速有效的去除大部分污染物的特点,而被认为能用于污染现场的迅速修复治理,但当前对不同淋洗剂的淋洗应用潜力仍需要进一步深入研究。本研究为探讨淋洗法在修复铅锌厂周边重金属污染土壤的修复效果及淋洗后土壤的利用价值及其潜在环境风险,试验中采用振荡淋洗的方法比较了几种螯合剂、有机酸及无机酸等淋洗剂对不同污染程度土壤中Cd、Cu、Zn、Pb的去除效果,并用BCR连续提取法分析了淋洗前后土壤中各重金属形态的变化,最后通过黑麦草盆栽实验及土壤酶分析,探讨了土壤经淋洗后的潜在生态风险。主要研究结果如下:(1)EDTA、EDDS、EGTA、NTA等4种螯合剂对土壤重金属Cd、Cu、Zn、Pb的去除率各不相同,但Cd的去除率均呈现出EDTANTAEDDSEGTA的特点。对于Cd、Cu、Zn和Pb等重金属而言,EDTA是较理想的淋洗剂,EDTA在浓度100mmol/L、pH 4、淋洗时间24 h的条件下,对污染土壤中重金属离子的去除率分别达Cd 76.4%-91.0%、Cu 38.1%-42.5%、Zn 19.2%-57.0%、Pb 45.4%-52.0%。(2)比较了乙酸、草酸、酒石酸、柠檬酸等4种有机酸对土壤中Cd、Cu、Zn、Pb的去除效果,结果表明,随着浓度增加重金属去除率也增加,在0.1mol/L时,柠檬酸和酒石酸分别对重金属的去除率最大;淋洗过程中,柠檬酸对Cd、Cu、Zn、Pb的去除效果略好于酒石酸,但从4种有机酸总体的去除率来看,0.1mol/L的柠檬酸和酒石酸对Cd、Cu、Zn、Pb等4种重金属的去除效果最好,且柠檬酸更适合处理污染严重的区域3土壤,酒石酸适合淋洗区域污染较轻的区域1土壤。(3)相比以上4种有机酸,无机酸HCl对重金属有较好的去除率。对Cd、Cu、Zn、Pb等4种重金属而言,当HCl浓度为0.1mol/L时,4种重金属去除达到最大,其大小分别为Cd(88.3%)Zn(60%)Pb(44.1%)Cu(23.7%);强酸对土壤的结构和营养物质等理化性质造成很大的破坏,因此使用HCl存在较大的环境风险。(4)淋洗前后土壤中重金属的形态分析表明EDTA、NTA、酒石酸、柠檬酸淋洗能够有效去除酸溶态、可还原态等有效态的重金属,降低了土壤中的重金属生物有效性和对环境的影响。(5)土壤经过淋洗后,可以显著减少黑麦草对重金属的吸收,且与未淋洗土壤相比,EDTA和NTA淋洗后土壤种植黑麦草后土壤呼吸均未发生显著变化,EDTA淋洗后土壤酶活性比NTA淋洗后土壤酶活性要高;与柠檬酸相比,酒石酸淋洗土壤种植黑麦草后土壤呼吸作用和土壤酶活性大小均有所增加。(6)因此,在降低土壤中重金属含量的同时土壤能够再利用,鉴于上述分析,考虑EDTA、NTA、酒石酸、柠檬酸和HCl的成本价格、淋洗效率和土壤潜在利用价值等因素,可认为采用EDTA和柠檬酸淋洗修复重金属污染土壤具有一定的实用性,并且环境风险较小。
[Abstract]:In recent years, with the rapid development of mining and smelting industry, the waste residue containing heavy metals discharged in the process of non-ferrous metals smelting will enter the soil through various ways, resulting in the destruction of the surrounding soil ecosystem and the decline of soil environmental quality. Among many remediation technologies for contaminated soils, leaching is considered to be a rapid remediation method for contaminated sites because it can remove most of the contaminants quickly and effectively. However, the potential of different leaching agents still needs further study. Remediation effect of leaching method on heavy metal contaminated soil around Pb-Zn plant and its potential environmental risk were discussed. The removal effects of several chelating agents, organic acids and inorganic acids on Cd, Cu, Zn and Pb in different contaminated soils were compared by oscillating leaching method. The removal efficiency of Cd, Cu, Zn and Pb in the soil was continuously extracted by BCR. The main results are as follows: (1) The removal rates of Cd, Cu, Zn and Pb by EDTA, EDDS, EGTA and NTA are different, but the removal rates of Cd, Zn and Pb are different. EDTA is an ideal eluent for heavy metals such as Cd, Cu, Zn and Pb. Under the conditions of 100 mmol/L, pH 4 and 24 h of elution time, the removal rates of heavy metal ions in contaminated soil by EDTA are 76.4% - 91.0%, 38.1% - 42.5%, 19.2% - 57.0% for Zn and 45.4% - 52.0% for Pb, respectively. The results showed that the removal efficiency of Cd, Cu, Zn and Pb increased with the increase of concentration, and the removal efficiency of citric acid and tartaric acid was the highest at 0.1 mol/L. The removal efficiency of Cd, Cu, Zn and Pb by citric acid was slightly better than that by tartaric acid during the leaching process. According to the total removal rate of acid, 0.1 mol/L citric acid and tartaric acid had the best removal effect on four heavy metals, such as Cd, Cu, Zn, Pb, and citric acid was more suitable for the treatment of three soils in the heavily polluted area, while tartaric acid was suitable for the treatment of one soil in the lightly polluted area. (3) Compared with the above four organic acids, HCl had a better removal rate of heavy metals. For four heavy metals, such as Cd, Cu, Zn and Pb, when HCl concentration was 0.1 mol/L, the removal of the four heavy metals reached the maximum, the size of which was Cd (88.3%) Zn (60%) Pb (44.1%) Cu (23.7%); strong acid caused great damage to soil structure and nutrient properties, so the use of HCl had a greater environmental risk. (4) Heavy gold in soil before and after leaching. Morphological analysis showed that EDTA, NTA, tartaric acid and citric acid leaching could effectively remove acid-soluble and reducible heavy metals, and reduce the bioavailability of heavy metals in soil and their impact on the environment. (5) After leaching, the uptake of heavy metals by ryegrass could be significantly reduced, and EDTA and citric acid leaching could reduce the bioavailability of heavy metals in soil and the environmental impact. Soil respiration did not change significantly after NTA leaching, and soil enzyme activity after EDTA leaching was higher than that after NTA leaching. Compared with citric acid, soil respiration and soil enzyme activity increased after planting Lolium perenne under tartaric acid leaching. In view of the above analysis, considering the cost price of EDTA, NTA, tartaric acid, citric acid and HCl, the leaching efficiency and the potential utilization value of soil, it can be concluded that EDTA and citric acid leaching for remediation of heavy metal contaminated soil has certain practicability and less environmental risk.
【学位授予单位】：西北农林科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X53

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