摘要:
矿区不当开采导致下游土壤As污染(As含量达到194 00mg/kg),研究了柠檬酸、氮川三乙酸三钠(NTA)、乙二胺二琥珀酸-三钠盐(EDDS)3种天然螯合剂清洗修复As污染土壤的效果以及清洗对As化学形态的影响,并探讨了清洗动力学过程。结果表明,柠檬酸、NTA和EDDS的最佳清洗条件:液土比分别为30、30和15mL/g,浓度分别为0.2、0.05和0.1mol/L,pH分别为2.67、13和13,震荡清洗时间分别为6、3和2h,对应的去除率为88.70%、94.05%和89.89%。运用吸附动力学模型对As的清洗动力学数据进行拟合,准一级方程拟合决定系数达到0.982 07,是描述柠檬酸清洗过程的最佳方程;NTA和EDDS则是准二级方程,NTA分段拟合的决定系数分别为0.999 04和0.940 37,EDDS对应为0.97825和0.816 92。3种天然螯合剂对碳酸盐结合态、铁锰氧化物结合态、有机结合态和残渣态均有40%~90%的去除率,其中NTA对铁锰氧化物结合态和残渣态的去除率分别为91.24%和95.03%,显著高于柠檬酸和EDDS
关键词:
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土壤清洗
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砷
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天然螯合剂
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动力学
Abstract:
Undeserved exploitation in the mining areas leads to the soils in the downstream contaminated by Arsenic (As content reaches to 19400 mg/kg). The effects of three natural chelating agents including citric acid, nitrilotriacetic acid trisodium salt (NTA) and trisodium (S,S)-ethylenediamine-N,N'- disuccinate(EDDS) on remediation of As-contaminated soils by flushing and the influence of flushing on the chemical speciation of As are studied. The kinetic process of flushing is also discussed. The results show that the best conditions for flushing with citric acid, NTA and EDDS are listed as follows:ratio of liquid to soil is 30, 30 and 15 mL/g respectively; concentration of the flushing fluid is 0.2, 0.05 and 0.1 mol/L; pH is 2.67, 13 and 13; time for vibration flushing is 6, 3 and 2 hours, with corresponding removal efficiency of 88.70%, 94.05% and 89.89% respectively. Adsorption kinetic equations are employed to describe the kinetic process. The results indicate that as the best equation for description of the washing process with citric acid, the pseudo first-order kinetics model fits well the experimental data of citric acid that R2 is 0.98207. However, the pseudo second-order equation fits well the experimental data of NTA and EDDS. R2 of NTA in two stages is 0.99904 and 0.94037, and that of EDDS is 0.97825 and 0.81692 respectively. With regard to the three natural chelating agents, the removal efficiency of carbonate bound, iron and manganese oxide bound, organic fraction and residue is all about 40%~90%. As for NTA, the removal efficiency of iron and manganese oxide bound and residue is 91.24% and 95.03%, significantly higher than the effects of citric acid and EDDS.
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