| This paper study about adsorption mechanism of antibiotic drugs using modified sludge, activated carbon. Gatifloxacin is choosen as adsorbate because that as new generation of antibiotics it is representative. We chose two types of sludge in the experiments, one come from sedimentation tank while the other from the deslimer. And then they are modified by ZnCl2, which can make the sludge expand and have more millipore. The fly ash is modified by HC1. The data is fitting with many kinds of isotherm equation model and kinetic equation model in order to analyze the mechanism of gatifloxacin. Also we do calculation of thermodynamic parameters to research the reaction thermal and reaction direaction. The results show:1) these adsorbents is certain effective for adsorption of gatifloxacin, their adsorption capacity is different in this order:activated carbon> modified sludge1> modified sludge2. The adsorption capacity of modified sludge is worse than that of activated carbon, but it has reach the acceptable level.2) Using linear isotherm model, Freundlich isotherm model and Langmuir isotherm model to fit the experimental results, we can see that almost all these adsorbents can be fit well by Freundlich adsorption isotherm equation. From the results, it is obvious that adsorption is a non-linear process, it is not only constrained by the allocation process, but also by the proliferation of internal, more in line with the "two-phase" model; it is a two-stage adsorption phenomenon. From value of RL, we know that langmuir isotherm can also be used to describe the adsorption process, which can prove the single-layer adsorption.3) From adsorption kinetics analysis, it can be seen that the adsorption dynamic characteristics of these adsorbents is great difference, such as adsorption rate and control steps. Modified sludge and activated carbon are more complex, control by many steps.4) The effects experiments of Ca2+on the adsorption of those adsorbent revealed the effect of ionic strength on adsorption of gatifloxacin process. Results show that different adsorbents has different response for Ca2+and it is relative with the nature of adsorbent. In addition, low concentration of Ca2+affects the adsorbates less than high concentration. Different Zeta potential makes the performance different when Ca2+concentration changes. Adsorption modified sludge is suppressed at low ionic strength, but increase ionic strength, adsorption increased, which may be related to the increase in the Zeta potential. 5) Doing thermodynamic analysis of the experimental data, it can be get that adsorption free energy△G which is a manifestation of the adsorption driving force are all negative in this experiment, that is to say adsorption of those adsorbent is a spontaneous reaction process; In addition, the adsorption reaction is different with general reaction, gatifloxacin adsorption increased as the temperature increased, the adsorption hea(?) H is positive, the reaction is endothermic, the adsorption entropy change△S is also become smaller. This phenomenon can be explained by replacement theory; through the value of△H and△G absolute, we know that the adsorption of those adsorbent is the result of physical adsorption and chemical adsorption, but physical adsorption plays a leading role. |
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