| 摘要: |
| 【目的】研究三氯乙酸（TCA）与黄土化学作用对其渗透性能的影响机理，为防止TCA渗流对地下水的污染提供参考。【方法】以杨凌黄土为研究对象，采用压汞试验，测定不同质量分数TCA溶液（0%（纯水），2%和8%）污染黄土孔隙分布密度、孔隙率和平均孔径的变化；采用土柱渗透试验，测定不同质量分数TCA溶液对黄土渗透特性和水分运移的影响；通过浑浊度试验、X射线衍射试验和扫描电镜观察，从上覆溶液的浊度演化、黄土胶结的腐蚀程度和表层颗粒的结构形态等角度对TCA在黄土中的渗透规律进行分析。【结果】当TCA质量分数由0%增加到8%时，TCA污染土中孔径0.1~1.0 μm孔隙的分布密度减小，孔隙率由25.2%上升至40.4%，平均孔径由0.28 μm升至0.34 μm，TCA对黄土同时表现出团聚性和腐蚀性。2% TCA溶液有利于黄土表层颗粒团聚，间接扩大渗流路径，使上覆溶液可以快速入渗，其在土柱中的渗流耗时是纯水的70%，有效增大了黄土的渗透性。8% TCA溶液破坏了黄土的胶结结构，使黄土表层的团聚颗粒分散为悬浮颗粒，悬浮颗粒的沉降和浊流入渗堵塞了渗流路径，从而在土壤表层形成了1~3 cm厚的不透水层，土颗粒之间生成的针状和片状氯化物结晶进一步堵塞孔隙并降低了溶液的入渗速率，其在土柱中的渗流耗时是纯水的3.6倍，明显降低了黄土渗透性。【结论】质量分数2%和8% TCA溶液对黄土渗透性影响不同，TCA污染的预防和治理需考虑TCA团聚、腐蚀行为对黄土渗透性的影响。 |
| 关键词: 农药污染 三氯乙酸；黄土；土柱渗透试验；渗透机理 |
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| 基金项目:陕西省自然科学基础研究计划项目（2020JQ-278）；中央高校基本科研业务费专项（2452019062）；陕西省博士后科研基金项目（2018BSHEDZZ23） |
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| Penetration mechanism of trichloroacetic acid in loess |
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LIU Hao,YANG Xiujuan,FAN Henghui,et al
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| Abstract: |
| 【Objective】The influence mechanism of chemical interaction between trichloroacetic acid (TCA) and loess on its permeability was studied to provide reference for preventing groundwater pollution by TCA seepage.【Method】The changes of pore distribution,porosity and average pore size of loess from Yangling contaminated by different TCA solutions (0%(pure water),2% and 8%) were measured by MIP test.Soil column infiltration test was used to determine the effects of TCA solution with different mass fractions on loess permeability and water transport.Through turbidity test,X-ray diffraction test and SEM observation,the permeability of TCA in loess was analyzed from the perspectives of turbidity evolution of overburden solution,corrosion degree of loess cementation and structural morphology of surface particles.【Result】When the mass fraction of TCA increased from 0% to 8%,the distribution density of pores with pore size between 0.1－1.0 μm decreased,the porosity increased from 25.2% to 40.4%,and the average pore size increased from 0.28 μm to 0.34 μm.TCA showed both agglomeration and corrosivity to loess.The 2% TCA solution was beneficial to the agglomeration of loess surface particles,indirectly expanded the seepage path,and enabled the overlying solution to penetrate quickly.The seepage time of the 2% TCA solution in the soil column was 70% of the pure water,which effectively increased the permeability of loess.The 8% TCA solution destroyed the cementation of loess structure and dispersed the loess surface particle dispersion to suspended particles.The settlement of suspended particles and turbidity current infiltration blocked the seepage path,and soil impervious layer with thickness of 1-3 cm was formed in the surface layer. Soil particles generated between needle and flake chloride crystallization further clogged pores and reduced the infiltration rate of solution.The seepage time in soil column was 3.6 times of that of pure water,indicating that the permeability of loess was significantly reduced.【Conclusion】TCA solutions with mass fractions of 2% and 8% had different effects on loess permeability.The prevention and treatment of TCA pollution should consider the effects of TCA agglomeration and corrosion on loess permeability. |
| Key words: pesticide pollution trichloroacetic acid loess soil column permeability test penetration mechanism |
