【作者】 林珍珠；

【导师】 王果；

【作者基本信息】 福建农林大学 ， 土壤学， 2009， 硕士

【摘要】 本研究以龙岩市新罗区特钢厂附近的Pb-Zn-Cd复合污染土壤为对象,采用连续提取的方法研究了HCl、柠檬酸和Na2-EDTA三种较常用的淋洗剂对Cd、Pb、Zn、Cu的去除效果,包括淋洗浓度和淋洗次数。其中,淋洗剂浓度为0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16 mol.L-1,淋洗次数为五次。根据各淋洗剂对这四种重金属的综合去除效果选择一种较优的淋洗剂,同时确定最适浓度和淋洗次数。以此淋洗组合为基础,进而研究淋洗工艺的优化以及淋洗废液的处置。研究结果如下:(1)三种淋洗剂各自对该土壤的较优淋洗浓度和淋洗次数分别为:HCl,0.1mol.L-1,2次;柠檬酸,0.08mol.L-1,2次;Na2-EDTA,0.02mol.L-1,1次。其中,Na2-EDTA对Pb的提取效率最高,但它价格较贵且淋洗后残留在土壤中不易降解。相比于HCl,柠檬酸除了对Cd的去除效率比HCl高以外,对Pb、Zn、Cu的去除率都比HCl低,综合去除率明显低于HCl。而且柠檬酸的成本也比HCl高。HCl对Zn和Cu的去除率比其它两种淋洗剂要高,且成本低廉。虽然用HCl做为淋洗剂会破坏土壤结构,而且会损失土壤中一些重要的营养元素,但通过常用的农业措施可以补偿。因此,选择0.1mol.L-1HCl去除土壤中的Cd、Pb、Zn、Cu,淋洗次数为2次。(2)淋洗条件经优化后确定为:液固比为2.5:1,210r.min-1振荡速度,振荡时间2h,淋洗2次。优化后,单次淋洗Pb、Zn、Cd、Cu的去除效率均比优化前提高,增幅分别为13.30%,9.07%,31.18%,28.22%。(3)相比于Na2S,选择CaO来去除淋洗废液中的重金属,更经济可行,且易于操作。使用Na2S时,会产生H2S,安全技术要求相对较高。使用CaO处理废液时,调pH至7-9即可。处理后的淋洗液即可直接排放或经酸化可回用。淋洗后的土壤可回填,沉淀的重金属及少量土壤可在垃圾场填埋。更多还原

【Abstract】 The effects of three washing solutions, HCl, citric acid and Na2-EDTA, for removing Cd, Pb Zn and Cu from a Pb-Zn-Cd polluted soil colleted from a field near a smelter were studied in order to select a best washing solution. The extractibility of the washing solutions at each washing was compared to set a suitable concentration and washing number for each washing solution. The soil was successively washed for 5 times with each solution of which the concentrations were 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16 mol.L-1, respectively. The optimal conditions for the selected washing solution and the treatment of the leachate solution were also studied. The main results were as follows:The suitable concentrations, washing number and removal efficiencies for removing Cd, Pb and Zn from this soil by the solutions were: HCl, 0.1mol.L-1, twice; citric acid, 0.08mol.L-1, twice; Na2-EDTA, 0.02mol.L-1. Na2-EDTA solution was more effective than the other two solutions in removing Pb but it is the most expensive and its residues in soils are difficult to be degraded so it is not the most suitable washing solution. As compared with HCl, citric acid solution was more effective in removing Cd while less effective in removing Pb and Zn. For the more, Citric acid is more expensive than HCl. HCl had higher extractibility in removing Zn and lower cost than citric acid. Although washing with HCl solution will seriously destroy soil structures and remove other necessary nutrients, the adverse effects can be reclaimed by common soil improvement practices. Therefore, 0.1mol.L-1 HCl with two washings was the best for removing Cd, Pb, Zn and Cu from the soil.The suitable technical conditions for washing Cd, Pb, Zn and Cu with 0.1 mol.L-1 HCl from the soil were as follows: solution/soil ratio=2.5:1; shake speed=210r.min-1; reaction time=2h; washing number=twice.With the optimal washing conditons, the removal rate of Pb, Zn, Cd and Cu by 0.1 mol.L-1 HCl were significantly raised to 27.23%, 19.61%, 59.61% and 19.73%, respectively.In comparison with Na2S, CaO was found to be more economical and easy to operation in removing metal ions from the acidic leachate solution. When Na2S was added to the acidic solution, H2S gas which is difficult to protected produced. When CaO solution is used to treat the acidic leachate solution, it is enough to adjust the solution to pH 7-9. After the treatment with CaO, the leachate solution can be discharged directly or reused after acidification.The clean soil can be reused as agricultural soil while the precipitates including heavy metals and some fine particles can be landfilled.更多还原