【作者】 王磊；

【导师】 孙成；

【作者基本信息】 南京大学 ， 环境科学， 2012， 硕士

【摘要】 老化过程是影响有机污染物在土壤中迁移转化及生物有效性的重要因素。研究有机污染物在土壤中的老化过程及其影响因素对污染物的生态风险评价、土壤质量标准制定和污染土壤的修复具有重要的意义。本论文以对硝基氯苯(p-NCB)为目标污染物,研究了p-NCB在土壤中不同条件下的老化过程。在“固-气-液”三相体系中,研究了土壤湿度对p-NCB在土壤中老化过程的影响,并通过土壤成分实验进一步考察影响的内在机制；在“固-液”二相体系中,研究了p-NCB在土壤上的长期吸附和多步解吸,以及吸附时间对解吸延滞性的影响。论文对p-NCB在土壤中的老化过程及其影响因素进行了初步探索,取得的主要结论如下：一、通过将实验土壤进行加标污染物和控制湿度的方法研究了土壤湿度对p-NCB在土壤中老化过程的影响。结果表明,土壤湿度造成p-NCB在两种土样上的提取率较干燥土样大为减小。土壤成分实验表明,高岭土中p-NCB的提取率受样品湿度的影响较大,腐殖酸的存在大大减小了湿度对老化过程的影响。提取率在反应21天后开始变缓,说明p-NCB在湿土壤样品上的老化分为两个阶段：自反应开始至21天是快速老化阶段,之后为缓慢老化阶段。p-NCB在干土样上的老化过程不明显,在实验周期下未发现提取率随反应时间有明显下降。二、通过批量平衡实验研究了p-NCB在两种土壤和腐殖酸上长期吸附和解吸行为。结果表明,吸附等温线随吸附时间会发生微小的变化,吸附量和吸附等温线的非线性都随吸附时间的延长而有所增加,反映了吸附剂的异质性随着吸附时间的延长而更加明显。证实了土壤中存在着一些难以被低浓度吸附质在短期内就能达到的吸附位点。吸附与解吸速率受溶质浓度的影响,低浓度时达到平衡所需的时间较长,高浓度时达到平衡的时间较短。解吸时,随着吸附浓度的增加,难以解吸的部分在总吸附量中占据的比例减小。三、p-NCB在两种土壤上都很难解吸,两步解吸所得的等温线与吸附等温线均不能互相重合,说明吸附存在很强的不可逆性,这可能是由于p-NCB与土壤中的非提取性有机质和“矿物-有机质”复合体之间的较强结合所致。而尽管p-NCB在腐殖酸上的吸附具有明显的非线性(n=0.794),但连续四步解吸所得的等温线与吸附等温线均能重合,说明p-NCB在腐殖酸上的吸附是可逆的。四、p-NCB在东北黑土上吸附不同时间(1天和36天)的吸附等温线重合,说明吸附平衡在1天内就已达到,但在随后进行的解吸实验中却发现两份样品的解吸等温线差别显著。推测可能是吸附达到表观平衡后p-NCB分子和黑土有机质随接触时间的增加发生类似于生物学上酶催化反应中的“诱导-契合”作用,从而使二者的结合更加紧密。高浓度的p-NCB可能会造成黑土有机质产生“条件效应”导致本身的结构变形,从而造成高浓度的p-NCB存在着显著的解吸延滞性。更多还原

【Abstract】 Aging of organic contaminants is an important factor affecting their fates and bioavailability. Research on the aging behavior of organic contaminants is helpful for ecological risk evaluation, soil quality assessment and remediation of contaminated soils.In this dissertation, some experiments were made for the aging progress of p-Nitrochlorobenzene (p-NCB) on three soils with different physicochemical properties under different conditions. In the three phase "solid-gas-liquid" system, the effects of soil moisture contents on aging progress of p-NCB in two soils and the soil compartment (e.g. Gaolinite, Humic acids and their complex) were studied to explore the inner mechanisms. In the two phase "solid-liquid" systems, the long-term sorption and desorption of p-NCB on soils and the effect of sorption time on desorption hysteresis were also investigated. The main results and conclusions were as follows:1. The effect of soil moisture on aging of p-NCB was conducted by supplication and moisture control of the soil samples. The results showed that soil moisture made the extractability of p-NCB on soils reduced considerably. In the soil compartment experiments, we have found that the effect of sample moisture on the extractability of p-NCB in gaolinite was the maximum. The exist of humic acids eliminated the effect of sample moisture contents. The decrease of extractability of p-NCB after21days reaction was hardly detected, suggesting that aging of p-NCB on soils was distributed to two stage:from the beginning to less than21days was the fast aging stage, and after that was the slow one. To our surprise, the extractability of p-NCB on the dry samples was almost the same as the beginning after120days experiment, suggesting that aging of p-NCB was not obvious on the dry soil samples.2. Long-term sorption and multi-steps desorption of p-NCB on two soils and humic acids were conducted using bath equilibrium experiments. The results showed that both sorption amount and nonlinearity of sorption isotherm were time-dependent, which were increased as the sorption time prolonged, suggesting the apparent heterogeneous of the sorbent was more obvious when the sorption time was longer. The results confirmed that there were some inner sorption sites in the soil particles which needed long time to reach for the sorbates. Initial aqueous concentration had great effect on the sorption rates of p-NCB. It needed more time to reach equilibrium for the lower concentration samples than for the higher ones. As the concentration increased, the difficult-desorption part was decreased.3. The sorbed p-NCB on the two soils was difficult to desorb, both the one-and two-steps desorption isotherms could not overlap with the sorption isotherm, indicating the strong sorption hysteresis of p-NCB on the two soils. That was attributed to the strong combination of p-NCB with non-extractable organic matter and organic matter-mineral complex. As concerned with the humic acids, although the sorption of p-NCB on them presented a nonlinear characteristic (n=0.794), the one-to four-steps desorption isotherms were almost overlapped with the sorption isotherm, suggesting sorption of p-NCB on humic acids was inversible.4. Sorption isotherms of p-NCB on Black soil for different time (1day and36days) were overlapped, suggesting the apparent sorption equilibrium was achieved in1day. But the desorption isotherms under the same condition were considerable different. Maybe after sorption achieving equilibrium, the interactions which were similar to "induced-fit" effect in biological enzyme catalytic reaction between p-NCB molecules and the soil organic matter were became much stronger as the reaction time prolonged. Sorption hysteresis was observed in high concentration range, the soil organic matter might be deformed by the high concentration sorbate.更多还原