Baup S, Wolbert D, Laplanche A
Laboratoire Chimie des Nuisances et Génie de l'Environnement-E.N.S.C. Rennes, Avenue du Général Leclerc, F-35700 Rennes, France.
Environ Technol. 2002 Oct;23(10):1107-17. doi: 10.1080/09593332308618339.
Three pesticides (atrazine, bromoxynil and diuron) and two granular activated carbons are involved in equilibrium and kinetic adsorption experiments. Equilibrium is represented by Freundlich isotherm law and kinetic is described by the Homogeneous Surface Diffusion Model, based on external mass transfer and intraparticle surface diffusion. Equilibrium and long-term experiments are conducted to compare Powdered Activated Carbon and Granular Activated Carbon. These first investigations show that crushing GAC into PAC improves the accessibility of the adsorption sites without increasing the number of these sites. In a second part, kinetics experiments are carried out using a Differential Column Batch Reactor. Thanks to this experimental device, the external mass transfer coefficient k(f) is calculated from empirical correlation and the effect of external mass transfer on adsorption is likely to be minimized. In order to obtain the intraparticle surface diffusion coefficient D. for these pesticides, comparisons between experimental kinetic data and simulations are conducted and the best agreement leads to the Ds coefficient. This procedure appears to be an efficient way to acquire surface diffusion coefficients for the adsorption of pesticides onto GAC. Finally it points out the role of surface diffusivity in the adsorption rate. As a matter of fact, even if the amount of the target-compound that could be potentially adsorbed is really important, its surface diffusion coefficient may be small, so that its adsorption may not have enough contact time to be totally achieved.
三种农药（莠去津、溴苯腈和敌草隆）以及两种颗粒活性炭参与了平衡吸附和动力学吸附实验。平衡吸附由弗伦德利希等温线定律表示，动力学吸附则由基于外部传质和颗粒内表面扩散的均相表面扩散模型描述。进行了平衡吸附实验和长期实验，以比较粉末活性炭和颗粒活性炭。这些初步研究表明，将颗粒活性炭粉碎成粉末活性炭可提高吸附位点的可及性，但不会增加这些位点的数量。在第二部分中，使用微分柱间歇式反应器进行动力学实验。借助该实验装置，根据经验关联式计算外部传质系数k(f)，并尽量减小外部传质对吸附的影响。为了获得这些农药在颗粒内的表面扩散系数D.，对实验动力学数据和模拟结果进行了比较，最佳拟合结果得出Ds系数。该方法似乎是获取农药在颗粒活性炭上吸附的表面扩散系数的有效途径。最后，指出了表面扩散率在吸附速率中的作用。事实上，即使潜在可吸附的目标化合物量很大，但其表面扩散系数可能很小，因此其吸附可能没有足够的接触时间来完全实现。
