Desorption kinetics of phenanthrene in aquifer material lacks hysteresis
Desorption kinetics of phenanthrene in aquifer material lacks hysteresis
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DOI：
10.1021/es034846p
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发表时间：
2004-08-01
影响因子：
11.4
通讯作者：
Grathwohl, P
中科院分区：
文献类型：
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作者：
Kleineidam, S;R端gner, H;Grathwohl, P
在长期吸附批量实验（20℃下长达 1010 天；Rugner, H.；Kleineidam, S.；Grathwohl, P. Long-term sorbdynamics of fenanthrene in aquifer Materials. Environ. Sci. Technol. 1999, 33, 1645-1651）之后，在流过柱中进行了解吸实验，以阐明含水层材料中菲的吸附/解吸滞后现象。本研究中使用的大多数吸附剂（从含水层沉积物或新鲜岩石碎片中分离出的均质岩石成分）由于嵌入颗粒内部的煤颗粒而表现出高度非线性的吸附等温线。由于吸附容量很高，因此在长达 1010 天的初始吸附吸收实验中，大多数吸附剂都没有达到吸附平衡。在 20 摄氏度下研究解吸长达 90 天。之后，对于选定的样品，温度从最初的20℃逐步升高到30℃、40℃、50℃，最后升高到70℃，以估计解吸的活化能。使用数值颗粒内孔扩散模型来拟合吸附吸收数据，并随后对解吸柱实验中的释放速率进行纯正向预测。解吸最初很快，随后是延长的拖尾，在其他研究中使用多速率一阶模型进行拟合。我们的结果表明，延迟颗粒内孔扩散模型可以使用独立于长期批量吸附实验获得的单个扩散速率常数来预测解吸速率。没有发现滞后现象的证据，这表明早期报道的许多滞后现象是由非平衡效应和“非物理”模型引起的实验假象。不同的温度步骤允许额外计算解吸活化能（45-59 W mol(-1)），这与延迟孔扩散过程的早期研究结果相当一致。此外，在 20 和 40 摄氏度下测定平衡吸附等温线，以比较吸附和解吸焓。两者非常一致，证实解吸与吸附没有显着差异。
Desorption experiments were carried out in flow through columns following long-term sorption batch experiments (up to 1010 days at 20 degreesC; Rugner, H.; Kleineidam, S.; Grathwohl, P. Long-term sorption kinetics of phenanthrene in aquifer materials. Environ. Sci. Technol. 1999, 33, 1645-1651) to elucidate sorption/desorption hysteresis phenomena of phenanthrene in aquifer materials. Most of the sorbents employed in this study (homogeneous lithocomponents separated from aquifer sediments or fresh rock fragments) showed highly nonlinear sorption isotherms because of coal particles embedded inside the grains. Because sorption capacities were high, sorption equilibrium was not reached in most of the sorbents during the initial sorptive uptake experiments lasting up to 1010 days. Desorption was studied up to 90 days at 20 degreesC. The temperature was raised after that stepwise from originally 20 to 30, 40, 50, and finally to 70 degreesC for selected samples to estimate activation energies of desorption. A numerical intraparticle pore diffusion model was used to fit sorptive uptake data and subsequently for pure forward prediction of the release rates in the desorption column experiments. Desorption was initially fast followed by extended tailing which in other studies is fitted by using multirate first-order models. Our results demonstrate that the retarded intraparticle pore diffusion model can predict the desorption rates with a single diffusion rate constant obtained independently from the long-term batch sorption experiment. No evidence for hysteresis was found, suggesting that many hysteresis phenomena reported earlier are experimental artifacts resulting from nonequilibrium effects and "nonphysical" models. The different temperature steps allowed one to additionally calculate activation energies of desorption (45-59 W mol(-1)), which were in reasonably good agreement with results from earlier studies for a retarded pore diffusion process. In addition, equilibrium sorption isotherms were determined at 20 and 40 degreesC to compare sorption and desorption enthalpies. Both were in good agreement, confirming that desorption was not significantly different from sorption.